485BPOS

As filed with the Securities and Exchange Commission on April 11, 2014

Securities Act of 1933 Registration No. 2-80543

Investment Company Act of 1940 Registration No. 811-03605

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 [X]

Pre-Effective Amendment No.                         [    ]

Post-Effective Amendment No. 74                  [X]

and/or

REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY ACT OF 1940

Amendment No. 89             [X]

(Check appropriate box or boxes)

NORTHERN INSTITUTIONAL FUNDS

(Exact Name of Registrant as Specified in Charter)

50 South LaSalle Street

Chicago, Illinois 60603

(Address of Principal Executive Offices)

800-637-1380

(Registrant’s Telephone Number, including Area Code)

Name and Address of Agent for Service: Diana E. McCarthy Drinker Biddle & Reath LLP One Logan Square, Suite 2000 Philadelphia, Pennsylvania 19103-6996 with a copy to: Craig R. Carberry, Secretary The Northern Trust Company 50 South LaSalle Street, MB-09 Chicago, Illinois 60603

It Is Proposed That This Filing Become Effective (Check Appropriate Box):

[X] immediately upon filing pursuant to paragraph (b)

[    ] On [date] pursuant to paragraph (b)

[    ] 60 days after filing pursuant to paragraph (a)(1)

[    ] On (date) pursuant to paragraph (a)(1)

[    ] 75 days after filing pursuant to paragraph (a)(2)

[    ] On (date) pursuant to paragraph (a)(2)

If appropriate, check the following box:

[    ] This post-effective amendment designates a new effective date for a previously filed post-effective amendment.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, as amended (the “Securities Act”), and the Investment Company Act of 1940, as amended, the Registrant certifies that it meets all of the requirements for effectiveness of this Post-Effective Amendment No. 74 to its Registration Statement under Rule 485(b) under the Securities Act and has duly caused this Post-Effective Amendment No. 74 to its Registration Statement to be signed on its behalf by the undersigned, duly authorized, in the City of Chicago and State of Illinois on the 11th day of April, 2014.

NORTHERN INSTITUTIONAL FUNDS
By:	/s/ Lloyd A. Wennlund
	Lloyd A. Wennlund
	President

Pursuant to the requirements of the Securities Act, this Post-Effective Amendment No. 74 to Registrant’s Registration Statement has been signed below by the following persons in the capacities and on the date indicated.

Name	Title	Date
/s/ Lloyd A. Wennlund	President (Principal	April 11, 2014
Lloyd A. Wennlund	Executive Officer)
/s/ Randal Rein	Treasurer	April 11, 2014
Randal Rein	(Principal Financial Officer and Principal Accounting Officer)
/s/ William L. Bax	Trustee	April 11, 2014
William L. Bax
/s/ Edward J. Condon, Jr.	Trustee	April 11, 2014
Edward J. Condon, Jr.
/s/ Mark G. Doll	Trustee	April 11, 2014
Mark G. Doll
/s/ Sandra Polk Guthman	Trustee	April 11, 2014
Sandra Polk Guthman
/s/ Stephen N. Potter	Trustee	April 11, 2014
Stephen N. Potter
/s/ Mary Jacobs Skinner	Trustee	April 11, 2014
Mary Jacobs Skinner
/s/ Richard P. Strubel	Trustee	April 11, 2014
Richard P. Strubel
/s/ Casey J. Sylla	Trustee	April 11, 2014
Casey J. Sylla

Exhibit Index

Exhibit No.	Description
EX-101. INS	XBRL Instance Document
EX-101.SCH	XBRL Taxonomy Extension Schema Document
EX-101.CAL	XBRL Taxonomy Extension Calculation Linkbase
EX-101.DEF	XBRL Taxonomy Extension Definition Linkbase
EX-101.LAB	XBRL Taxonomy Extension Labels Linkbase
EX-101.PRE	XBRL Taxonomy Extension Presentation Linkbase

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	NORTHERN INSTITUTIONAL FUNDS
Prospectus Date	rr_ProspectusDate	Apr. 01, 2014
Service and Premier Shares | NORTHERN INSTITUTIONAL TAX-EXEMPT PORTFOLIO
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	TAX-EXEMPT PORTFOLIO
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to provide, to the extent consistent with the preservation of capital and prescribed portfolio standards, a high level of income exempt from regular federal income tax by investing primarily in municipal instruments.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE PORTFOLIO
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold Service and Premier Shares of the Portfolio.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Portfolio Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	April 1, 2015
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following Example is intended to help you compare the cost of investing in the Service and Premier Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Portfolio seeks to achieve its objective by investing primarily in high quality short-term municipal instruments, the interest on which is exempt from regular federal income tax. The high level of income sought by the Portfolio is relative to yields currently available in the tax-exempt marketplace. Municipal instruments may include: Fixed, variable and floating rate notes and similar debt instruments; Asset-backed securities that are considered municipal instruments (such as trust certificates backed by municipal bonds); Tax-exempt commercial paper; Municipal bonds, notes, paper or other instruments; and Municipal bonds and notes that are guaranteed as to principal and interest or backed by the U.S. government or by its agencies, instrumentalities or sponsored enterprises. Except in extraordinary circumstances, at least 80% of the Portfolio’s net assets will be invested in debt instruments that pay interest that is exempt from regular federal income tax. Alternative minimum tax (“AMT”) obligations, which pay interest that may be treated as an item of tax preference to shareholders under the federal AMT, will not be deemed to be eligible debt instruments for the purposes of determining whether the Portfolio meets this policy. To the extent that the Portfolio invests in AMT obligations, a limited portion of the Portfolio’s dividends may be subject to federal income tax for shareholders subject to AMT. The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio. During extraordinary market conditions and interest rate environments, all or any portion of the Portfolio’s assets may be uninvested or invested in taxable instruments. Uninvested assets do not generate income. The Portfolio may not achieve its investment objective during this time.
Risk [Heading]	rr_RiskHeading	PRINCIPAL RISKS
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share. INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher. GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio. PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities. DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities. INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities. MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results. CREDIT (OR DEFAULT) RISK is the risk that the inability or unwillingness of an issuer or guarantor of a fixed-income security, or a counterparty to a repurchase or other transaction, to meet its payment or other financial obligations will adversely affect the value of the Portfolio’s investments and its yield. Changes in the credit rating of a debt security held by the Portfolio could have a similar effect. PROJECT/INDUSTRIAL DEVELOPMENT BOND RISK is the risk that the Portfolio may be more sensitive to an adverse economic, business or political development if it invests more than 25% of its assets in municipal instruments, the interest upon which is paid solely from revenues of similar projects, or in industrial development bonds. TAX RISK is the risk that future legislative or administrative changes or court decisions may materially affect the value of municipal instruments or the ability of the Portfolio to pay tax-exempt dividends. MUNICIPAL MARKET VOLATILITY RISK is the risk that the Portfolio may be adversely affected by the volatile municipal market. The municipal market can be significantly affected by adverse tax, legislative, or political changes and the financial condition of the issuers of municipal securities. An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Lose Money [Text]	rr_RiskLoseMoney	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Money Market Fund [Text]	rr_RiskMoneyMarketFund	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	PORTFOLIO PERFORMANCE
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Service Shares from year to year. There are no Premier Shares currently outstanding for the Portfolio. The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future. Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio's Service Shares from year to year.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800-637-1380
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	www.northerninstitutionalfunds.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	CALENDAR YEAR TOTAL RETURN (SERVICE SHARES)*
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	* For the periods shown in the bar chart above, the highest quarterly return was 0.79% in the second quarter of 2007, and the lowest quarterly return was 0.00% in the fourth quarter of 2013.
Performance Table Heading	rr_PerformanceTableHeading	AVERAGE ANNUAL TOTAL RETURNS (For the periods ended December 31, 2013)
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	The 7-day yield for Service Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.
Money Market Seven Day Yield Phone	rr_MoneyMarketSevenDayYieldPhone	800-637-1380
Service and Premier Shares | NORTHERN INSTITUTIONAL TAX-EXEMPT PORTFOLIO | Service Shares
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fees	rr_ManagementFeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.39%
Administration Fees	rr_Component1OtherExpensesOverAssets	0.10%
Service Agent Fees	rr_Component2OtherExpensesOverAssets	0.25%
Other Operating Expenses	rr_Component3OtherExpensesOverAssets	0.04%
Total Annual Portfolio Operating Expenses	rr_ExpensesOverAssets	0.64%
Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.03%)	[1]
Total Annual Portfolio Operating Expenses	rr_NetExpensesOverAssets	0.61%	[2]
1 Year	rr_ExpenseExampleYear01	62
3 Years	rr_ExpenseExampleYear03	202
5 Years	rr_ExpenseExampleYear05	354
10 Years	rr_ExpenseExampleYear10	796
2004	rr_AnnualReturn2004	0.65%
2005	rr_AnnualReturn2005	1.84%
2006	rr_AnnualReturn2006	2.86%
2007	rr_AnnualReturn2007	3.08%
2008	rr_AnnualReturn2008	1.74%
2009	rr_AnnualReturn2009	0.11%
2010	rr_AnnualReturn2010	0.02%
2011	rr_AnnualReturn2011	0.02%
2012	rr_AnnualReturn2012	0.01%
2013	rr_AnnualReturn2013	0.01%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2007
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	0.79%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2013
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	0.00%
1-Year	rr_AverageAnnualReturnYear01	0.01%
5-Year	rr_AverageAnnualReturnYear05	0.04%
10-Year	rr_AverageAnnualReturnYear10	1.03%
Since Inception	rr_AverageAnnualReturnSinceInception	1.33%
Inception Date	rr_AverageAnnualReturnInceptionDate	May 13, 1999
Money Market Seven Day Yield, Caption [Text]	rr_MoneyMarketSevenDayYieldCaption	The 7-day yield for Service Shares of the Portfolio as of December 31, 2013:
Money Market Seven Day Yield	rr_MoneyMarketSevenDayYield	0.01%
Service and Premier Shares | NORTHERN INSTITUTIONAL TAX-EXEMPT PORTFOLIO | Premier Shares
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fees	rr_ManagementFeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.65%
Administration Fees	rr_Component1OtherExpensesOverAssets	0.10%
Service Agent Fees	rr_Component2OtherExpensesOverAssets	0.50%
Other Operating Expenses	rr_Component3OtherExpensesOverAssets	0.05%
Total Annual Portfolio Operating Expenses	rr_ExpensesOverAssets	0.90%
Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.03%)	[1]
Total Annual Portfolio Operating Expenses	rr_NetExpensesOverAssets	0.87%	[2]
1 Year	rr_ExpenseExampleYear01	89
3 Years	rr_ExpenseExampleYear03	284
5 Years	rr_ExpenseExampleYear05	496
10 Years	rr_ExpenseExampleYear10	$ 1,105

[1] Northern Trust Investments, Inc. has contractually agreed to reimburse certain expenses of the Portfolio (including the administration fee, but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses, acquired fund fees and expenses, a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries, expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio's "Other Expenses" exceed 0.10%. This contractual limitation may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Expense Reimbursement

XML

Service and Premier Shares | NORTHERN INSTITUTIONAL MUNICIPAL PORTFOLIO

MUNICIPAL PORTFOLIO

INVESTMENT OBJECTIVE

The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to provide, to the extent consistent with the preservation of capital, a high level of income exempt from regular federal income tax by investing primarily in municipal instruments. This objective may be changed without shareholder approval.

FEES AND EXPENSES OF THE PORTFOLIO

This table describes the fees and expenses that you may pay if you buy and hold Service and Premier Shares of the Portfolio.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees Service and Premier Shares NORTHERN INSTITUTIONAL MUNICIPAL PORTFOLIO (USD $)	Service Shares	Premier Shares
Shareholder Fees (fees paid directly from your investment)	none	none

Annual Portfolio Operating Expenses (expenses that you pay each year as
a percentage of the value of your investment)

Annual Fund Operating Expenses Service and Premier Shares NORTHERN INSTITUTIONAL MUNICIPAL PORTFOLIO		Service Shares	Premier Shares
Management Fees		0.20%	0.20%
Other Expenses		0.38%	0.64%
Administration Fees		0.10%	0.10%
Service Agent Fees		0.25%	0.50%
Other Operating Expenses		0.03%	0.04%
Total Annual Portfolio Operating Expenses		0.58%	0.84%
Fee Waiver and Expense Reimbursement	[1]	(0.12%)	(0.12%)
Total Annual Portfolio Operating Expenses	[2]	0.46%	0.72%

EXAMPLE

The following Example is intended to help you compare the cost of investing in the Service and Premier Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Service and Premier Shares NORTHERN INSTITUTIONAL MUNICIPAL PORTFOLIO (USD $)	1 Year	3 Years	5 Years	10 Years
Service Shares	47	174	312	714
Premier Shares	74	256	454	1,026

PRINCIPAL INVESTMENT STRATEGIES

The Portfolio seeks to achieve its objective by investing primarily in high quality short-term municipal instruments, the interest on which is exempt from regular federal income tax. The high level of income sought by the Portfolio is relative to yields currently available in the tax-exempt marketplace. Municipal instruments may include:

• Fixed, variable and floating rate notes and similar debt instruments;

• Asset-backed securities that are considered municipal instruments (such as trust certificates backed by municipal bonds);

• Tax-exempt commercial paper;

• Municipal bonds, notes, paper or other instruments; and

• Municipal bonds and notes that are guaranteed as to principal and interest or backed by the U.S. government or by its agencies, instrumentalities or sponsored enterprises.

Except in extraordinary circumstances, at least 80% of the Portfolio’s net assets will be invested in debt instruments that pay interest that is exempt from regular federal income tax. Alternative minimum tax (“AMT”) obligations, which pay interest that may be treated as an item of tax preference to shareholders under the federal AMT, will be deemed eligible investments for the purposes of determining whether the portfolio meets this policy. To the extent that the Portfolio invests in AMT obligations, a significant portion of the Portfolio’s dividends may be subject to federal income tax for shareholders subject to AMT. The Portfolio is not limited in the amount of its assets that may be invested in AMT obligations.

The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio.

During extraordinary market conditions and interest rate environments, all or any portion of the Portfolio’s assets may be held uninvested or invested in taxable instruments. Uninvested assets do not generate income. The Portfolio may not achieve its investment objective during this time.

PRINCIPAL RISKS

STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share.

INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher.

GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio.

PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities.

DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities.

INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities.

MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results.

CREDIT (OR DEFAULT) RISK is the risk that the inability or unwillingness of an issuer or guarantor of a fixed-income security, or a counterparty to a repurchase or other transaction, to meet its payment or other financial obligations will adversely affect the value of the Portfolio’s investments and its yield. Changes in the credit rating of a debt security held by the Portfolio could have a similar effect.

PROJECT/INDUSTRIAL DEVELOPMENT BOND RISK is the risk that the Portfolio may be more sensitive to an adverse economic, business or political development if it invests more than 25% of its assets in municipal instruments, the interest upon which is paid solely from revenues of similar projects, or in industrial development bonds.

TAX RISK is the risk that future legislative or administrative changes or court decisions may materially affect the value of municipal instruments or the ability of the Portfolio to pay tax-exempt dividends.

MUNICIPAL MARKET VOLATILITY RISK is the risk that the Portfolio may be adversely affected by the volatile municipal market. The municipal market can be significantly affected by adverse tax, legislative, or political changes and the financial condition of the issuers of municipal securities.

An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.

PORTFOLIO PERFORMANCE

The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Service Shares from year to year. There are no Premier Shares currently outstanding for the Portfolio.

The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.

Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.

CALENDAR YEAR TOTAL RETURN (SERVICE SHARES)*

* For the periods shown in the bar chart above, the highest quarterly return was 0.83% in the third quarter of 2007, and the lowest quarterly return was 0.00% in the third quarter of 2013.

AVERAGE ANNUAL TOTAL RETURNS
(For the periods ended December 31, 2013)

Average Annual Total Returns	Inception Date	1-Year	5-Year	10-Year	Since Inception
Service and Premier Shares NORTHERN INSTITUTIONAL MUNICIPAL PORTFOLIO Service Shares	Feb. 11, 2000	0.02%	0.05%	1.11%	1.34%

The 7-day yield for Service Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.

[1] Northern Trust Investments, Inc. has contractually agreed to limit the management fees charged to the Portfolio to 0.10% of the Portfolio's average daily net assets and to reimburse certain expenses of the Portfolio (including the administration fee, but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses, acquired fund fees and expenses, a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries, expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio's "Other Expenses" exceed 0.10%. These contractual limitations may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Fee Waiver and Expense Reimbursement

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	NORTHERN INSTITUTIONAL FUNDS
Prospectus Date	rr_ProspectusDate	Apr. 01, 2014
Service and Premier Shares | NORTHERN INSTITUTIONAL U.S. GOVERNMENT PORTFOLIO
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	U.S. GOVERNMENT PORTFOLIO
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to maximize current income to the extent consistent with the preservation of capital and maintenance of liquidity by investing exclusively in high quality money market instruments.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE PORTFOLIO
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold Service and Premier Shares of the Portfolio.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Portfolio Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	April 1, 2015
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following Example is intended to help you compare the cost of investing in the Service and Premier Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Portfolio seeks to achieve its objective by investing, under normal circumstances, substantially all (and at least 80%) of its net assets in securities issued or guaranteed as to principal and interest by the U.S. government or by its agencies, instrumentalities or sponsored enterprises, and repurchase agreements backed by such securities. The Portfolio makes significant investments in securities issued by U.S. government-sponsored entities. Such securities are neither issued nor guaranteed by the U.S. Treasury. Under unusual circumstances, as when appropriate U.S. government securities and repurchase agreements backed by such securities are unavailable, the Portfolio also may invest in cash equivalents, including money market funds. The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio. During extraordinary market conditions and interest rate environments, all or any portion of the Portfolio’s assets may be uninvested and will therefore not generate income. The Portfolio may not achieve its investment objective during this time.
Risk [Heading]	rr_RiskHeading	PRINCIPAL RISKS
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share. INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher. GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio. PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities. DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities. INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities. MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results. U.S. GOVERNMENT SECURITIES RISK is the risk that the U.S. government will not provide financial support to its agencies, instrumentalities or sponsored enterprises if it is not obligated to do so by law. Many U.S. government securities purchased by the Portfolio are not backed by the full faith and credit of the United States. It is possible that the issuers of such securities will not have the funds to meet their payment obligations in the future. An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Lose Money [Text]	rr_RiskLoseMoney	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Money Market Fund [Text]	rr_RiskMoneyMarketFund	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	PORTFOLIO PERFORMANCE
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Service Shares from year to year. There are no Premier Shares currently outstanding for the Portfolio. The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future. Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Service Shares from year to year.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800-637-1380
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	www.northerninstitutionalfunds.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	CALENDAR YEAR TOTAL RETURN (SERVICE SHARES)*
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	* For the periods shown in the bar chart above, the highest quarterly return was 1.18% in the fourth quarter of 2006, and the lowest quarterly return was 0.00% in the fourth quarter of 2013.
Performance Table Heading	rr_PerformanceTableHeading	AVERAGE ANNUAL TOTAL RETURNS (For the periods ended December 31, 2013)
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	The 7-day yield for Service Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.
Money Market Seven Day Yield Phone	rr_MoneyMarketSevenDayYieldPhone	800-637-1380
Service and Premier Shares | NORTHERN INSTITUTIONAL U.S. GOVERNMENT PORTFOLIO | Service Shares
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fees	rr_ManagementFeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.38%
Administration Fees	rr_Component1OtherExpensesOverAssets	0.10%
Service Agent Fees	rr_Component2OtherExpensesOverAssets	0.25%
Other Operating Expenses	rr_Component3OtherExpensesOverAssets	0.03%
Total Annual Portfolio Operating Expenses	rr_ExpensesOverAssets	0.63%
Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.02%)	[1]
Total Annual Portfolio Operating Expenses	rr_NetExpensesOverAssets	0.61%	[2]
1 Year	rr_ExpenseExampleYear01	62
3 Years	rr_ExpenseExampleYear03	200
5 Years	rr_ExpenseExampleYear05	349
10 Years	rr_ExpenseExampleYear10	784
2004	rr_AnnualReturn2004	0.79%
2005	rr_AnnualReturn2005	2.65%
2006	rr_AnnualReturn2006	4.48%
2007	rr_AnnualReturn2007	4.60%
2008	rr_AnnualReturn2008	1.74%
2009	rr_AnnualReturn2009	0.03%
2010	rr_AnnualReturn2010	0.02%
2011	rr_AnnualReturn2011	0.02%
2012	rr_AnnualReturn2012	0.01%
2013	rr_AnnualReturn2013	0.01%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Dec. 31, 2006
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	1.18%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2013
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	0.00%
1-Year	rr_AverageAnnualReturnYear01	0.01%
5-Year	rr_AverageAnnualReturnYear05	0.02%
10-Year	rr_AverageAnnualReturnYear10	1.42%
Since Inception	rr_AverageAnnualReturnSinceInception	1.96%
Inception Date	rr_AverageAnnualReturnInceptionDate	Apr. 01, 1999
Money Market Seven Day Yield, Caption [Text]	rr_MoneyMarketSevenDayYieldCaption	The 7-day yield for Service Shares of the Portfolio as of December 31, 2013:
Money Market Seven Day Yield	rr_MoneyMarketSevenDayYield	0.01%
Service and Premier Shares | NORTHERN INSTITUTIONAL U.S. GOVERNMENT PORTFOLIO | Premier Shares
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fees	rr_ManagementFeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.64%
Administration Fees	rr_Component1OtherExpensesOverAssets	0.10%
Service Agent Fees	rr_Component2OtherExpensesOverAssets	0.50%
Other Operating Expenses	rr_Component3OtherExpensesOverAssets	0.04%
Total Annual Portfolio Operating Expenses	rr_ExpensesOverAssets	0.89%
Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.02%)	[1]
Total Annual Portfolio Operating Expenses	rr_NetExpensesOverAssets	0.87%	[2]
1 Year	rr_ExpenseExampleYear01	89
3 Years	rr_ExpenseExampleYear03	282
5 Years	rr_ExpenseExampleYear05	491
10 Years	rr_ExpenseExampleYear10	$ 1,094

[1] Northern Trust Investments, Inc. has contractually agreed to reimburse certain expenses of the Portfolio (including the administration fee, but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses, acquired fund fees and expenses, a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries, expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio's "Other Expenses" exceed 0.10%. This contractual limitation may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Expense Reimbursement

XML

Shares, Service and Premier Shares | NORTHERN INSTITUTIONAL PRIME OBLIGATIONS PORTFOLIO

PRIME OBLIGATIONS PORTFOLIO

INVESTMENT OBJECTIVE

The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to maximize current income to the extent consistent with the preservation of capital and maintenance of liquidity by investing exclusively in high quality money market instruments.

FEES AND EXPENSES OF THE PORTFOLIO

This table describes the fees and expenses that you may pay if you buy and hold shares of the Portfolio.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees Shares, Service and Premier Shares NORTHERN INSTITUTIONAL PRIME OBLIGATIONS PORTFOLIO (USD $)	Shares	Service Shares	Premier Shares
Shareholder Fees (fees paid directly from your investment)	none	none	none

Annual Portfolio Operating Expenses (expenses that you pay each year as
a percentage of the value of your investment)

Annual Fund Operating Expenses Shares, Service and Premier Shares NORTHERN INSTITUTIONAL PRIME OBLIGATIONS PORTFOLIO		Shares	Service Shares	Premier Shares
Management Fees		0.15%	0.15%	0.15%
Other Expenses		0.12%	0.38%	0.64%
Administration Fees		0.10%	0.10%	0.10%
Service Agent Fees		none	0.25%	0.50%
Other Operating Expenses		0.02%	0.03%	0.04%
Total Annual Portfolio Operating Expenses		0.27%	0.53%	0.79%
Fee Waiver and Expense Reimbursement	[1]	(0.12%)	(0.12%)	(0.12%)
Total Annual Portfolio Operating Expenses	[2]	0.15%	0.41%	0.67%

EXAMPLE

The following Example is intended to help you compare the cost of investing in shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Shares, Service and Premier Shares NORTHERN INSTITUTIONAL PRIME OBLIGATIONS PORTFOLIO (USD $)	1 Year	3 Years	5 Years	10 Years
Shares	15	75	140	331
Service Shares	42	158	284	653
Premier Shares	68	240	427	967

PRINCIPAL INVESTMENT STRATEGIES

The Portfolio seeks to achieve its objective by investing in a broad range of high-quality, U.S. dollar-denominated government, bank and commercial obligations that are available in the money markets, including:

• Obligations of U.S. banks (including obligations of foreign branches of such banks);

• Obligations of foreign commercial banks;

• Commercial paper and other obligations issued or guaranteed by U.S. and foreign corporations and other issuers;

• Corporate bonds, notes, paper and other instruments that are of high quality;

• Asset-backed securities and asset-backed commercial paper;

• Securities issued or guaranteed as to principal and interest by the U.S. government or by its agencies, instrumentalities or sponsored enterprises and custodial receipts with respect thereto;

• Securities issued or guaranteed by one or more foreign governments or political subdivisions, agencies or instrumentalities;

• Repurchase agreements; and

• Municipal securities issued or guaranteed by state or local governmental bodies.

The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio.

During extraordinary market conditions and interest rate environments, all or any portion of the Portfolio’s assets may be uninvested and will therefore not generate income. The Portfolio may not achieve its investment objective during this time.

PRINCIPAL RISKS

STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share.

INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher.

CREDIT (OR DEFAULT) RISK is the risk that the inability or unwillingness of an issuer or guarantor of a fixed-income security, or a counterparty to a repurchase or other transaction, to meet its payment or other financial obligations will adversely affect the value of the Portfolio’s investments and its yield. Changes in the credit rating of a debt security held by the Portfolio could have a similar effect.

GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio.

INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities.

MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results.

PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities.

DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities.

FOREIGN SECURITIES RISK is the risk that a foreign security, even if it is a U.S. dollar-denominated foreign security, could lose value as a result of political, financial and economic events in foreign countries, less stringent foreign securities regulations and accounting and disclosure standards or other factors.

An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.

PORTFOLIO PERFORMANCE

The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Shares from year to year. There are no Premier Shares currently outstanding for the Portfolio.

The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.

Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.

CALENDAR YEAR TOTAL RETURN (SHARES)*

*For the periods shown in the bar chart above, the highest quarterly return was 1.31% in the third quarter of 2007, and the lowest quarterly return was 0.00% in the fourth quarter of 2013.

AVERAGE ANNUAL TOTAL RETURNS
(For the periods ended December 31, 2013)

Average Annual Total Returns Shares, Service and Premier Shares NORTHERN INSTITUTIONAL PRIME OBLIGATIONS PORTFOLIO	Inception Date	1-Year	5-Year	10-Year	Since Inception
Shares	Aug. 21, 2003	0.05%	0.15%	1.73%	1.70%
Service Shares	Sep. 02, 2003	0.05%	0.07%	1.56%	1.53%

The 7-day yield for Shares of the Portfolio as of December 31, 2013: 0.02%. The 7-day yield for Service Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.

[1] Northern Trust Investments, Inc. has contractually agreed to limit the management fees charged to the Portfolio to 0.10% of the Portfolio's average daily net assets and to reimburse certain expenses of the Portfolio (including the administration fee, but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses, acquired fund fees and expenses, a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries, expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio's "Other Expenses" exceed 0.05%. These contractual limitations may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc. serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Fee Waiver and Expense Reimbursement

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	NORTHERN INSTITUTIONAL FUNDS
Prospectus Date	rr_ProspectusDate	Apr. 01, 2014
Service and Premier Shares | NORTHERN INSTITUTIONAL TREASURY PORTFOLIO
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	TREASURY PORTFOLIO
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to maximize current income to the extent consistent with the preservation of capital and maintenance of liquidity by investing primarily in U.S. Treasury securities, securities guaranteed as to principal and interest by the U.S. government, and related repurchase agreements.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE PORTFOLIO
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold Service and Premier Shares of the Portfolio.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Portfolio Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	April 1, 2015
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following Example is intended to help you compare the cost of investing in the Service and Premier Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Portfolio seeks to achieve its objective by investing, under normal circumstances, its net assets exclusively in: Short-term bills, notes and other obligations issued or guaranteed by the U.S. Treasury (“Treasury Obligations”); Repurchase agreements with counterparties collateralized fully by Treasury Obligations; and Shares of other money market portfolios of regulated investment companies that i) limit investments to U.S. Treasury Obligations and related repurchase agreements, and ii) determine NAVs based on Rule 2a-7 under the Investment Company Act of 1940, as amended (the “1940 Act”). The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio. In addition, during extraordinary market conditions and interest rate environments, all or any portion of the Portfolio’s assets may be uninvested and will therefore not generate income. The Portfolio may not achieve its investment objective during this time.
Risk [Heading]	rr_RiskHeading	PRINCIPAL RISKS
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share. INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher. GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio. PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities. DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities. INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities. MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results. CREDIT (OR DEFAULT) RISK is the risk that the inability or unwillingness of an issuer or guarantor of a fixed-income security, or a counterparty to a repurchase or other transaction, to meet its payment or other financial obligations will adversely affect the value of the Portfolio’s investments and its yield. Changes in the credit rating of a debt security held by the Portfolio could have a similar effect. An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Lose Money [Text]	rr_RiskLoseMoney	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Money Market Fund [Text]	rr_RiskMoneyMarketFund	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	PORTFOLIO PERFORMANCE
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Shares from year to year. There are no Service Shares or Premier Shares currently outstanding for the Portfolio. For this reason, the performance information shown below is only for Shares, which are offered in a separate Prospectus. Service Shares and Premier Shares would have similar annual returns when compared with Shares because Shares, Service Shares and Premier Shares are invested in the same portfolio of securities. The annual returns of Shares would differ from those of Service Shares and Premier Shares only to the extent that the classes do not have the same expenses. The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future. Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Shares from year to year.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800-637-1380
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	www.northerninstitutionalfunds.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	CALENDAR YEAR TOTAL RETURN (SHARES)*
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	* For the periods shown in the bar chart above, the highest quarterly return was 0.05% in the first quarter of 2009, and the lowest quarterly return was 0.00% in the fourth quarter of 2013.
Bar Chart, Returns for Class Not Offered in Prospectus [Text]	rr_BarChartReturnsForClassNotOfferedInProspectus	There are no Service Shares or Premier Shares currently outstanding for the Portfolio. For this reason, the performance information shown below is only for Shares, which are offered in a separate Prospectus. Service Shares and Premier Shares would have similar annual returns when compared with Shares because Shares, Service Shares and Premier Shares are invested in the same portfolio of securities. The annual returns of Shares would differ from those of Service Shares and Premier Shares only to the extent that the classes do not have the same expenses.
Performance Table Heading	rr_PerformanceTableHeading	AVERAGE ANNUAL TOTAL RETURNS (For the periods ended December 31, 2013)
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	The 7-day yield for Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.
Money Market Seven Day Yield Phone	rr_MoneyMarketSevenDayYieldPhone	800-637-1380
Service and Premier Shares | NORTHERN INSTITUTIONAL TREASURY PORTFOLIO | Service Shares
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fees	rr_ManagementFeesOverAssets	0.20%
Other Expenses	rr_OtherExpensesOverAssets	0.38%
Administration Fees	rr_Component1OtherExpensesOverAssets	0.10%
Service Agent Fees	rr_Component2OtherExpensesOverAssets	0.25%
Other Operating Expenses	rr_Component3OtherExpensesOverAssets	0.03%
Total Annual Portfolio Operating Expenses	rr_ExpensesOverAssets	0.58%
Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.12%)	[1]
Total Annual Portfolio Operating Expenses	rr_NetExpensesOverAssets	0.46%	[2]
1 Year	rr_ExpenseExampleYear01	47
3 Years	rr_ExpenseExampleYear03	174
5 Years	rr_ExpenseExampleYear05	312
10 Years	rr_ExpenseExampleYear10	714
Service and Premier Shares | NORTHERN INSTITUTIONAL TREASURY PORTFOLIO | Premier Shares
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fees	rr_ManagementFeesOverAssets	0.20%
Other Expenses	rr_OtherExpensesOverAssets	0.64%
Administration Fees	rr_Component1OtherExpensesOverAssets	0.10%
Service Agent Fees	rr_Component2OtherExpensesOverAssets	0.50%
Other Operating Expenses	rr_Component3OtherExpensesOverAssets	0.04%
Total Annual Portfolio Operating Expenses	rr_ExpensesOverAssets	0.84%
Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.12%)	[1]
Total Annual Portfolio Operating Expenses	rr_NetExpensesOverAssets	0.72%	[2]
1 Year	rr_ExpenseExampleYear01	74
3 Years	rr_ExpenseExampleYear03	256
5 Years	rr_ExpenseExampleYear05	454
10 Years	rr_ExpenseExampleYear10	$ 1,026
Service and Premier Shares | NORTHERN INSTITUTIONAL TREASURY PORTFOLIO | Shares
Risk/Return:	rr_RiskReturnAbstract
2009	rr_AnnualReturn2009	0.11%
2010	rr_AnnualReturn2010	0.07%
2011	rr_AnnualReturn2011	0.02%
2012	rr_AnnualReturn2012	0.02%
2013	rr_AnnualReturn2013	0.01%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Mar. 31, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	0.05%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2013
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	0.00%
1-Year	rr_AverageAnnualReturnYear01	0.01%
5-Year	rr_AverageAnnualReturnYear05	0.05%
Since Inception	rr_AverageAnnualReturnSinceInception	0.05%
Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 05, 2008
Money Market Seven Day Yield, Caption [Text]	rr_MoneyMarketSevenDayYieldCaption	The 7-day yield for Shares of the Portfolio as of December 31, 2013:
Money Market Seven Day Yield	rr_MoneyMarketSevenDayYield	0.01%

[1] Northern Trust Investments, Inc. has contractually agreed to limit the management fees charged to the Portfolio to 0.10% of the Portfolio's average daily net assets and to reimburse certain expenses of the Portfolio (including the administration fee, but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses, acquired fund fees and expenses, a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries, expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio's "Other Expenses" exceed 0.10%. These contractual limitations may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Fee Waiver and Expense Reimbursement

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	NORTHERN INSTITUTIONAL FUNDS
Prospectus Date	rr_ProspectusDate	Apr. 01, 2014
Service and Premier Shares | NORTHERN INSTITUTIONAL DIVERSIFIED ASSETS PORTFOLIO
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	DIVERSIFIED ASSETS PORTFOLIO
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to maximize current income to the extent consistent with the preservation of capital and maintenance of liquidity by investing exclusively in high quality money market instruments.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE PORTFOLIO
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold Service and Premier Shares of the Portfolio.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Portfolio Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	April 1, 2015
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following Example is intended to help you compare the cost of investing in the Service and Premier Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Portfolio seeks to achieve its objective by investing in a broad range of high-quality, U.S. dollar-denominated government, bank and commercial obligations that are available in the money markets, including: Obligations of U.S. banks (including obligations of foreign branches of such banks); Obligations of foreign commercial banks; Commercial paper and other obligations issued or guaranteed by U.S. and foreign corporations and other issuers; Corporate bonds, notes, paper and other instruments that are of high quality; Asset-backed securities and asset-backed commercial paper; Securities issued or guaranteed as to principal and interest by the U.S. government or by its agencies, instrumentalities or sponsored enterprises and custodial receipts with respect thereto; Securities issued or guaranteed by one or more foreign governments or political subdivisions, agencies or instrumentalities; Repurchase agreements; and Municipal securities issued or guaranteed by state or local governmental bodies. The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio. During extraordinary market conditions and interest rate environments, all or any portion of the Portfolio's assets may be uninvested and will therefore not generate income. The Portfolio may not achieve its investment objective during this time.
Risk [Heading]	rr_RiskHeading	PRINCIPAL RISKS
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share. INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher. GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio. PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities. DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities. INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities. MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results. CREDIT (OR DEFAULT) RISK is the risk that the inability or unwillingness of an issuer or guarantor of a fixed-income security, or a counterparty to a repurchase or other transaction, to meet its payment or other financial obligations will adversely affect the value of the Portfolio’s investments and its yield. Changes in the credit rating of a debt security held by the Portfolio could have a similar effect. FOREIGN SECURITIES RISK is the risk that a foreign security, even if it is a U.S. dollar-denominated foreign security, could lose value as a result of political, financial and economic events in foreign countries, less stringent foreign securities regulations and accounting and disclosure standards or other factors. An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Lose Money [Text]	rr_RiskLoseMoney	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Money Market Fund [Text]	rr_RiskMoneyMarketFund	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	PORTFOLIO PERFORMANCE
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Service Shares from year to year. There are no Premier Shares currently outstanding for the Portfolio. The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future. Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Service Shares from year to year.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800-637-1380
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	www.northerninstitutionalfunds.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	CALENDAR YEAR TOTAL RETURN (SERVICE SHARES)*
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	* For the periods shown in the bar chart above, the highest quarterly return was 1.20% in the third quarter of 2007, and the lowest quarterly return was 0.00% in the fourth quarter of 2013.
Performance Table Heading	rr_PerformanceTableHeading	AVERAGE ANNUAL TOTAL RETURNS (For the periods ended December 31, 2013)
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	The 7-day yield for Service Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.
Money Market Seven Day Yield Phone	rr_MoneyMarketSevenDayYieldPhone	800-637-1380
Service and Premier Shares | NORTHERN INSTITUTIONAL DIVERSIFIED ASSETS PORTFOLIO | Service Shares
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fees	rr_ManagementFeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.38%
Administration Fees	rr_Component1OtherExpensesOverAssets	0.10%
Service Agent Fees	rr_Component2OtherExpensesOverAssets	0.25%
Other Operating Expenses	rr_Component3OtherExpensesOverAssets	0.03%
Total Annual Portfolio Operating Expenses	rr_ExpensesOverAssets	0.63%
Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.02%)	[1]
Total Annual Portfolio Operating Expenses	rr_NetExpensesOverAssets	0.61%	[2]
1 Year	rr_ExpenseExampleYear01	62
3 Years	rr_ExpenseExampleYear03	200
5 Years	rr_ExpenseExampleYear05	349
10 Years	rr_ExpenseExampleYear10	784
2004	rr_AnnualReturn2004	0.82%
2005	rr_AnnualReturn2005	2.70%
2006	rr_AnnualReturn2006	4.53%
2007	rr_AnnualReturn2007	4.76%
2008	rr_AnnualReturn2008	1.83%
2009	rr_AnnualReturn2009	0.10%
2010	rr_AnnualReturn2010	0.02%
2011	rr_AnnualReturn2011	0.03%
2012	rr_AnnualReturn2012	0.01%
2013	rr_AnnualReturn2013	0.01%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2007
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	1.20%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2013
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	0.00%
1-Year	rr_AverageAnnualReturnYear01	0.01%
5-Year	rr_AverageAnnualReturnYear05	0.04%
10-Year	rr_AverageAnnualReturnYear10	1.46%
Since Inception	rr_AverageAnnualReturnSinceInception	2.16%
Inception Date	rr_AverageAnnualReturnInceptionDate	Jul. 01, 1998
Money Market Seven Day Yield, Caption [Text]	rr_MoneyMarketSevenDayYieldCaption	The 7-day yield for Service Shares of the Portfolio as of December 31, 2013:
Money Market Seven Day Yield	rr_MoneyMarketSevenDayYield	0.01%
Service and Premier Shares | NORTHERN INSTITUTIONAL DIVERSIFIED ASSETS PORTFOLIO | Premier Shares
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fees	rr_ManagementFeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.64%
Administration Fees	rr_Component1OtherExpensesOverAssets	0.10%
Service Agent Fees	rr_Component2OtherExpensesOverAssets	0.50%
Other Operating Expenses	rr_Component3OtherExpensesOverAssets	0.04%
Total Annual Portfolio Operating Expenses	rr_ExpensesOverAssets	0.89%
Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.02%)	[1]
Total Annual Portfolio Operating Expenses	rr_NetExpensesOverAssets	0.87%	[2]
1 Year	rr_ExpenseExampleYear01	89
3 Years	rr_ExpenseExampleYear03	282
5 Years	rr_ExpenseExampleYear05	491
10 Years	rr_ExpenseExampleYear10	$ 1,094

[1] Northern Trust Investments, Inc. has contractually agreed to reimburse certain expenses of the Portfolio (including the administration fee, but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses, acquired fund fees and expenses, a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries, expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio's "Other Expenses" exceed 0.10%. This contractual limitation may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Expense Reimbursement

XML

Shares | NORTHERN INSTITUTIONAL MUNICIPAL PORTFOLIO

MUNICIPAL PORTFOLIO

INVESTMENT OBJECTIVE

The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to provide, to the extent consistent with the preservation of capital, a high level of income exempt from regular federal income tax by investing primarily in municipal instruments. This objective may be changed without shareholder approval.

FEES AND EXPENSES OF THE PORTFOLIO

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Portfolio.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (USD $)	Shares NORTHERN INSTITUTIONAL MUNICIPAL PORTFOLIO
Shareholder Fees (fees paid directly from your investment)	none

Annual Portfolio Operating Expenses (expenses that you pay each year as
a percentage of the value of your investment)

Annual Fund Operating Expenses		Shares NORTHERN INSTITUTIONAL MUNICIPAL PORTFOLIO
Management Fees		0.20%
Other Expenses		0.12%
Administration Fees		0.10%
Service Agent Fees		none
Other Operating Expenses		0.02%
Total Annual Portfolio Operating Expenses		0.32%
Fee Waiver and Expense Reimbursement	[1]	(0.12%)
Total Annual Portfolio Operating Expenses	[2]	0.20%

EXAMPLE

The following Example is intended to help you compare the cost of investing in the Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)	1 Year	3 Years	5 Years	10 Years
Shares NORTHERN INSTITUTIONAL MUNICIPAL PORTFOLIO	20	91	168	394

PRINCIPAL INVESTMENT STRATEGIES

The Portfolio seeks to achieve its objective by investing primarily in high-quality short-term municipal instruments, the interest on which is exempt from regular federal income tax. The high level of income sought by the Portfolio is relative to yields currently available in the tax-exempt marketplace. Municipal instruments may include:

• Fixed, variable and floating rate notes and similar debt instruments;

• Asset-backed securities that are considered municipal instruments (such as trust certificates backed by municipal bonds);

• Tax-exempt commercial paper;

• Municipal bonds, notes, paper or other instruments; and

• Municipal bonds and notes that are guaranteed as to principal and interest or backed by the U.S. government or by its agencies, instrumentalities or sponsored enterprises.

Except in extraordinary circumstances, at least 80% of the Portfolio’s net assets will be invested in debt instruments that pay interest that is exempt from regular federal income tax. Alternative minimum tax (“AMT”) obligations, which pay interest that may be treated as an item of tax preference to shareholders under the federal AMT, will be deemed eligible investments for the purposes of determining whether the portfolio meets this policy. To the extent that the Portfolio invests in AMT obligations, a significant portion of the Portfolio’s dividends may be subject to federal income tax for shareholders subject to AMT. The Portfolio is not limited in the amount of its assets that may be invested in AMT obligations.

The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio.

During extraordinary market conditions and interest rate environments, all or any portion of the Portfolio’s assets may be uninvested or invested in taxable instruments. Uninvested assets do not generate income. The Portfolio may not achieve its investment objective during this time.

PRINCIPAL RISKS

STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share.

INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher.

GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio.

PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities.

DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities.

INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities.

MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results.

CREDIT (OR DEFAULT) RISK is the risk that the inability or unwillingness of an issuer or guarantor of a fixed-income security, or a counterparty to a repurchase or other transaction, to meet its payment or other financial obligations will adversely affect the value of the Portfolio’s investments and its yield. Changes in the credit rating of a debt security held by the Portfolio could have a similar effect.

PROJECT/INDUSTRIAL DEVELOPMENT BOND RISK is the risk that the Portfolio may be more sensitive to an adverse economic, business or political development if it invests more than 25% of its assets in municipal instruments, the interest upon which is paid solely from revenues of similar projects, or in industrial development bonds.

TAX RISK is the risk that future legislative or administrative changes or court decisions may materially affect the value of municipal instruments or the ability of the Portfolio to pay tax-exempt dividends.

MUNICIPAL MARKET VOLATILITY RISK is the risk that the Portfolio may be adversely affected by the volatile municipal market. The municipal market can be significantly affected by adverse tax, legislative, or political changes and the financial condition of the issuers of municipal securities.

An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.

PORTFOLIO PERFORMANCE

The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Shares from year to year.

The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.

Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.

CALENDAR YEAR TOTAL RETURN (SHARES)*

* For the periods shown in the bar chart above, the highest quarterly return was 0.89% in the third quarter of 2007, and the lowest quarterly return was 0.00% in the third quarter of 2013.

AVERAGE ANNUAL TOTAL RETURNS
(For the periods ended December 31, 2013)

Average Annual Total Returns	Inception Date	1-Year	5-Year	10-Year	Since Inception
Shares NORTHERN INSTITUTIONAL MUNICIPAL PORTFOLIO	Dec. 01, 1999	0.02%	0.12%	1.27%	1.56%

The 7-day yield for Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.

[1] Northern Trust Investments, Inc. has contractually agreed to limit the management fees charged to the Portfolio to 0.10% of the Portfolio’s average daily net assets and to reimburse certain expenses of the Portfolio (including the administration fee; but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses; acquired fund fees and expenses; a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries; expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio’s “Other Expenses” exceed 0.10%. These contractual limitations may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Fee Waiver and Expense Reimbursement

XML

Shares | NORTHERN INSTITUTIONAL U.S. GOVERNMENT PORTFOLIO

U.S. GOVERNMENT PORTFOLIO

INVESTMENT OBJECTIVE

The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to maximize current income to the extent consistent with the preservation of capital and maintenance of liquidity by investing exclusively in high quality money market instruments.

FEES AND EXPENSES OF THE PORTFOLIO

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Portfolio.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (USD $)	Shares NORTHERN INSTITUTIONAL U.S. GOVERNMENT PORTFOLIO
Shareholder Fees (fees paid directly from your investment)	none

Annual Portfolio Operating Expenses (expenses that you pay each year as
a percentage of the value of your investment)

Annual Fund Operating Expenses		Shares NORTHERN INSTITUTIONAL U.S. GOVERNMENT PORTFOLIO
Management Fees		0.25%
Other Expenses		0.12%
Administration Fees		0.10%
Service Agent Fees		none
Other Operating Expenses		0.02%
Total Annual Portfolio Operating Expenses		0.37%
Expense Reimbursement	[1]	(0.02%)
Total Annual Portfolio Operating Expenses	[2]	0.35%

EXAMPLE

The following Example is intended to help you compare the cost of investing in the Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)	1 Year	3 Years	5 Years	10 Years
Shares NORTHERN INSTITUTIONAL U.S. GOVERNMENT PORTFOLIO	36	117	206	466

PRINCIPAL INVESTMENT STRATEGIES

The Portfolio seeks to achieve its objective by investing, under normal circumstances, substantially all (and at least 80%) of its net assets in securities issued or guaranteed as to principal and interest by the U.S. government or by its agencies, instrumentalities or sponsored enterprises, and repurchase agreements backed by such securities.

The Portfolio makes significant investments in securities issued by U.S. government-sponsored entities. Such securities are neither issued nor guaranteed by the U.S. Treasury. Under unusual circumstances, as when appropriate U.S. government securities and repurchase agreements backed by such securities are unavailable, the Portfolio also may invest in cash equivalents, including money market funds.

The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio.

During extraordinary market conditions and interest rate environments, all or any portion of the Portfolio’s assets may be uninvested and will therefore not generate income. The Portfolio may not achieve its investment objective during this time.

PRINCIPAL RISKS

STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share.

INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher.

GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio.

PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities.

DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities.

INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities.

MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results.

U.S. GOVERNMENT SECURITIES RISK is the risk that the U.S. government will not provide financial support to its agencies, instrumentalities or sponsored enterprises if it is not obligated to do so by law. Many U.S. government securities purchased by the Portfolio are not backed by the full faith and credit of the United States. It is possible that the issuers of such securities will not have the funds to meet their payment obligations in the future.

An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.

PORTFOLIO PERFORMANCE

The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Shares from year to year.

The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.

Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.

CALENDAR YEAR TOTAL RETURN (SHARES)*

* For the periods shown in the bar chart above, the highest quarterly return was 1.25% in the fourth quarter of 2006, and the lowest quarterly return was 0.00% in the fourth quarter of 2013.

AVERAGE ANNUAL TOTAL RETURNS
(For the periods ended December 31, 2013)

Average Annual Total Returns	Inception Date	1-Year	5-Year	10-Year	Since Inception
Shares NORTHERN INSTITUTIONAL U.S. GOVERNMENT PORTFOLIO	Oct. 29, 1985	0.01%	0.03%	1.55%	3.86%

The 7-day yield for Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.

[1] Northern Trust Investments, Inc. has contractually agreed to reimburse certain expenses of the Portfolio (including the administration fee; but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses; acquired fund fees and expenses; a portion of the compensation paid to each Trustee who is not an officer; director or employee of Northern Trust Corporation or its subsidiaries; expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds; and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio’s “Other Expenses” exceed 0.10%. This contractual limitation may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Expense Reimbursement

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	NORTHERN INSTITUTIONAL FUNDS
Prospectus Date	rr_ProspectusDate	Apr. 01, 2014
Shares | NORTHERN INSTITUTIONAL MUNICIPAL PORTFOLIO
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	MUNICIPAL PORTFOLIO
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to provide, to the extent consistent with the preservation of capital, a high level of income exempt from regular federal income tax by investing primarily in municipal instruments. This objective may be changed without shareholder approval.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE PORTFOLIO
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold Shares of the Portfolio.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Portfolio Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	April 1, 2015
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following Example is intended to help you compare the cost of investing in the Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Portfolio seeks to achieve its objective by investing primarily in high-quality short-term municipal instruments, the interest on which is exempt from regular federal income tax. The high level of income sought by the Portfolio is relative to yields currently available in the tax-exempt marketplace. Municipal instruments may include: Fixed, variable and floating rate notes and similar debt instruments; Asset-backed securities that are considered municipal instruments (such as trust certificates backed by municipal bonds); Tax-exempt commercial paper; Municipal bonds, notes, paper or other instruments; and Municipal bonds and notes that are guaranteed as to principal and interest or backed by the U.S. government or by its agencies, instrumentalities or sponsored enterprises. Except in extraordinary circumstances, at least 80% of the Portfolio’s net assets will be invested in debt instruments that pay interest that is exempt from regular federal income tax. Alternative minimum tax (“AMT”) obligations, which pay interest that may be treated as an item of tax preference to shareholders under the federal AMT, will be deemed eligible investments for the purposes of determining whether the portfolio meets this policy. To the extent that the Portfolio invests in AMT obligations, a significant portion of the Portfolio’s dividends may be subject to federal income tax for shareholders subject to AMT. The Portfolio is not limited in the amount of its assets that may be invested in AMT obligations. The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio. During extraordinary market conditions and interest rate environments, all or any portion of the Portfolio’s assets may be uninvested or invested in taxable instruments. Uninvested assets do not generate income. The Portfolio may not achieve its investment objective during this time.
Risk [Heading]	rr_RiskHeading	PRINCIPAL RISKS
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share. INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher. GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio. PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities. DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities. INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities. MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results. CREDIT (OR DEFAULT) RISK is the risk that the inability or unwillingness of an issuer or guarantor of a fixed-income security, or a counterparty to a repurchase or other transaction, to meet its payment or other financial obligations will adversely affect the value of the Portfolio’s investments and its yield. Changes in the credit rating of a debt security held by the Portfolio could have a similar effect. PROJECT/INDUSTRIAL DEVELOPMENT BOND RISK is the risk that the Portfolio may be more sensitive to an adverse economic, business or political development if it invests more than 25% of its assets in municipal instruments, the interest upon which is paid solely from revenues of similar projects, or in industrial development bonds. TAX RISK is the risk that future legislative or administrative changes or court decisions may materially affect the value of municipal instruments or the ability of the Portfolio to pay tax-exempt dividends. MUNICIPAL MARKET VOLATILITY RISK is the risk that the Portfolio may be adversely affected by the volatile municipal market. The municipal market can be significantly affected by adverse tax, legislative, or political changes and the financial condition of the issuers of municipal securities. An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Lose Money [Text]	rr_RiskLoseMoney	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Money Market Fund [Text]	rr_RiskMoneyMarketFund	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	PORTFOLIO PERFORMANCE
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Shares from year to year. The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future. Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Shares from year to year.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800-637-1380
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	www.northerninstitutionalfunds.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	CALENDAR YEAR TOTAL RETURN (SHARES)*
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	* For the periods shown in the bar chart above, the highest quarterly return was 0.89% in the third quarter of 2007, and the lowest quarterly return was 0.00% in the third quarter of 2013.
Performance Table Heading	rr_PerformanceTableHeading	AVERAGE ANNUAL TOTAL RETURNS (For the periods ended December 31, 2013)
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	The 7-day yield for Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.
Money Market Seven Day Yield Phone	rr_MoneyMarketSevenDayYieldPhone	800-637-1380
Shares | NORTHERN INSTITUTIONAL MUNICIPAL PORTFOLIO | Shares
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fees	rr_ManagementFeesOverAssets	0.20%
Other Expenses	rr_OtherExpensesOverAssets	0.12%
Administration Fees	rr_Component1OtherExpensesOverAssets	0.10%
Service Agent Fees	rr_Component2OtherExpensesOverAssets	none
Other Operating Expenses	rr_Component3OtherExpensesOverAssets	0.02%
Total Annual Portfolio Operating Expenses	rr_ExpensesOverAssets	0.32%
Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.12%)	[1]
Total Annual Portfolio Operating Expenses	rr_NetExpensesOverAssets	0.20%	[2]
1 Year	rr_ExpenseExampleYear01	20
3 Years	rr_ExpenseExampleYear03	91
5 Years	rr_ExpenseExampleYear05	168
10 Years	rr_ExpenseExampleYear10	$ 394
2004	rr_AnnualReturn2004	1.06%
2005	rr_AnnualReturn2005	2.26%
2006	rr_AnnualReturn2006	3.29%
2007	rr_AnnualReturn2007	3.50%
2008	rr_AnnualReturn2008	2.10%
2009	rr_AnnualReturn2009	0.42%
2010	rr_AnnualReturn2010	0.11%
2011	rr_AnnualReturn2011	0.04%
2012	rr_AnnualReturn2012	0.02%
2013	rr_AnnualReturn2013	0.02%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2007
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	0.89%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2013
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	0.00%
1-Year	rr_AverageAnnualReturnYear01	0.02%
5-Year	rr_AverageAnnualReturnYear05	0.12%
10-Year	rr_AverageAnnualReturnYear10	1.27%
Since Inception	rr_AverageAnnualReturnSinceInception	1.56%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 01, 1999
Money Market Seven Day Yield, Caption [Text]	rr_MoneyMarketSevenDayYieldCaption	The 7-day yield for Shares of the Portfolio as of December 31, 2013:
Money Market Seven Day Yield	rr_MoneyMarketSevenDayYield	0.01%

[1] Northern Trust Investments, Inc. has contractually agreed to limit the management fees charged to the Portfolio to 0.10% of the Portfolio’s average daily net assets and to reimburse certain expenses of the Portfolio (including the administration fee; but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses; acquired fund fees and expenses; a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries; expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio’s “Other Expenses” exceed 0.10%. These contractual limitations may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Fee Waiver and Expense Reimbursement

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	NORTHERN INSTITUTIONAL FUNDS
Prospectus Date	rr_ProspectusDate	Apr. 01, 2014
Shares | NORTHERN INSTITUTIONAL TREASURY PORTFOLIO
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	TREASURY PORTFOLIO
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to maximize current income to the extent consistent with the preservation of capital and maintenance of liquidity by investing primarily in U.S. Treasury securities, securities guaranteed as to principal and interest by the U.S. government, and related repurchase agreements.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE PORTFOLIO
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold Shares of the Portfolio.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Portfolio Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	April 1, 2015
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following Example is intended to help you compare the cost of investing in the Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Portfolio seeks to achieve its objective by investing, under normal circumstances, its net assets exclusively in: Short-term bills, notes and other obligations issued or guaranteed by the U.S. Treasury (“Treasury Obligations”); Repurchase agreements with counterparties collateralized fully by Treasury Obligations; and Shares of other money market portfolios of regulated investment companies that i) limit investments to U.S. Treasury Obligations and related repurchase agreements, and ii) determine NAVs based on Rule 2a-7 under the Investment Company Act of 1940, as amended (the “1940 Act”). The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio. In addition, during extraordinary market conditions and interest rate environments, all or any portion of the Portfolio’s assets may be uninvested and will therefore not generate income. The Portfolio may not achieve its investment objective during this time.
Risk [Heading]	rr_RiskHeading	PRINCIPAL RISKS
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share. INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher. GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio. PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities. DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities. INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities. MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results. CREDIT (OR DEFAULT) RISK is the risk that the inability or unwillingness of an issuer or guarantor of a fixed-income security, or a counterparty to a repurchase or other transaction, to meet its payment or other financial obligations will adversely affect the value of the Portfolio’s investments and its yield. Changes in the credit rating of a debt security held by the Portfolio could have a similar effect. An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Lose Money [Text]	rr_RiskLoseMoney	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Money Market Fund [Text]	rr_RiskMoneyMarketFund	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	PORTFOLIO PERFORMANCE
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Shares from year to year. The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future. Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Shares from year to year.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800-637-1380
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	www.northerninstitutionalfunds.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	CALENDAR YEAR TOTAL RETURN (SHARES)*
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	* For the periods shown in the bar chart above, the highest quarterly return was 0.05% in the first quarter of 2009, and the lowest quarterly return was 0.00% in the fourth quarter of 2013.
Performance Table Heading	rr_PerformanceTableHeading	AVERAGE ANNUAL TOTAL RETURNS (For the periods ended December 31, 2013)
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	The 7-day yield for Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.
Money Market Seven Day Yield Phone	rr_MoneyMarketSevenDayYieldPhone	800-637-1380
Shares | NORTHERN INSTITUTIONAL TREASURY PORTFOLIO | Shares
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fees	rr_ManagementFeesOverAssets	0.20%
Other Expenses	rr_OtherExpensesOverAssets	0.12%
Administration Fees	rr_Component1OtherExpensesOverAssets	0.10%
Service Agent Fees	rr_Component2OtherExpensesOverAssets	none
Other Operating Expenses	rr_Component3OtherExpensesOverAssets	0.02%
Total Annual Portfolio Operating Expenses	rr_ExpensesOverAssets	0.32%
Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.12%)	[1]
Total Annual Portfolio Operating Expenses	rr_NetExpensesOverAssets	0.20%	[2]
1 Year	rr_ExpenseExampleYear01	20
3 Years	rr_ExpenseExampleYear03	91
5 Years	rr_ExpenseExampleYear05	168
10 Years	rr_ExpenseExampleYear10	$ 394
2009	rr_AnnualReturn2009	0.11%
2010	rr_AnnualReturn2010	0.07%
2011	rr_AnnualReturn2011	0.02%
2012	rr_AnnualReturn2012	0.02%
2013	rr_AnnualReturn2013	0.01%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Mar. 31, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	0.05%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2013
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	0.00%
1-Year	rr_AverageAnnualReturnYear01	0.01%
5-Year	rr_AverageAnnualReturnYear05	0.05%
Since Inception	rr_AverageAnnualReturnSinceInception	0.05%
Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 05, 2008
Money Market Seven Day Yield, Caption [Text]	rr_MoneyMarketSevenDayYieldCaption	The 7-day yield for Shares of the Portfolio as of December 31, 2013:
Money Market Seven Day Yield	rr_MoneyMarketSevenDayYield	0.01%

[1] Northern Trust Investments, Inc. has contractually agreed to limit the management fees charged to the Portfolio to 0.10% of the Portfolio’s average daily net assets and to reimburse certain expenses of the Portfolio (including the administration fee; but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses; acquired fund fees and expenses; a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries; expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio’s “Other Expenses” exceed 0.10%. These contractual limitations may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Fee Waiver and Expense Reimbursement

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	NORTHERN INSTITUTIONAL FUNDS
Prospectus Date	rr_ProspectusDate	Apr. 01, 2014
Document Creation Date	dei_DocumentCreationDate	Mar. 21, 2014

XML

Service and Premier Shares | NORTHERN INSTITUTIONAL DIVERSIFIED ASSETS PORTFOLIO

DIVERSIFIED ASSETS PORTFOLIO

INVESTMENT OBJECTIVE

The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to maximize current income to the extent consistent with the preservation of capital and maintenance of liquidity by investing exclusively in high quality money market instruments.

FEES AND EXPENSES OF THE PORTFOLIO

This table describes the fees and expenses that you may pay if you buy and hold Service and Premier Shares of the Portfolio.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees Service and Premier Shares NORTHERN INSTITUTIONAL DIVERSIFIED ASSETS PORTFOLIO (USD $)	Service Shares	Premier Shares
Shareholder Fees (fees paid directly from your investment)	none	none

Annual Portfolio Operating Expenses (expenses that you pay each year as
a percentage of the value of your investment)

Annual Fund Operating Expenses Service and Premier Shares NORTHERN INSTITUTIONAL DIVERSIFIED ASSETS PORTFOLIO		Service Shares	Premier Shares
Management Fees		0.25%	0.25%
Other Expenses		0.38%	0.64%
Administration Fees		0.10%	0.10%
Service Agent Fees		0.25%	0.50%
Other Operating Expenses		0.03%	0.04%
Total Annual Portfolio Operating Expenses		0.63%	0.89%
Expense Reimbursement	[1]	(0.02%)	(0.02%)
Total Annual Portfolio Operating Expenses	[2]	0.61%	0.87%

EXAMPLE

The following Example is intended to help you compare the cost of investing in the Service and Premier Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Service and Premier Shares NORTHERN INSTITUTIONAL DIVERSIFIED ASSETS PORTFOLIO (USD $)	1 Year	3 Years	5 Years	10 Years
Service Shares	62	200	349	784
Premier Shares	89	282	491	1,094

PRINCIPAL INVESTMENT STRATEGIES

The Portfolio seeks to achieve its objective by investing in a broad range of high-quality, U.S. dollar-denominated government, bank and commercial obligations that are available in the money markets, including:

• Obligations of U.S. banks (including obligations of foreign branches of such banks);

• Obligations of foreign commercial banks;

• Commercial paper and other obligations issued or guaranteed by U.S. and foreign corporations and other issuers;

• Corporate bonds, notes, paper and other instruments that are of high quality;

• Asset-backed securities and asset-backed commercial paper;

• Securities issued or guaranteed as to principal and interest by the U.S. government or by its agencies, instrumentalities or sponsored enterprises and custodial receipts with respect thereto;

• Securities issued or guaranteed by one or more foreign governments or political subdivisions, agencies or instrumentalities;

• Repurchase agreements; and

• Municipal securities issued or guaranteed by state or local governmental bodies.

The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio.

During extraordinary market conditions and interest rate environments, all or any portion of the Portfolio's assets may be uninvested and will therefore not generate income. The Portfolio may not achieve its investment objective during this time.

PRINCIPAL RISKS

STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share.

INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher.

GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio.

PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities.

DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities.

INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities.

MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results.

CREDIT (OR DEFAULT) RISK is the risk that the inability or unwillingness of an issuer or guarantor of a fixed-income security, or a counterparty to a repurchase or other transaction, to meet its payment or other financial obligations will adversely affect the value of the Portfolio’s investments and its yield. Changes in the credit rating of a debt security held by the Portfolio could have a similar effect.

FOREIGN SECURITIES RISK is the risk that a foreign security, even if it is a U.S. dollar-denominated foreign security, could lose value as a result of political, financial and economic events in foreign countries, less stringent foreign securities regulations and accounting and disclosure standards or other factors.

An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.

PORTFOLIO PERFORMANCE

The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Service Shares from year to year. There are no Premier Shares currently outstanding for the Portfolio.

The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.

Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.

CALENDAR YEAR TOTAL RETURN (SERVICE SHARES)*

* For the periods shown in the bar chart above, the highest quarterly return was 1.20% in the third quarter of 2007, and the lowest quarterly return was 0.00% in the fourth quarter of 2013.

AVERAGE ANNUAL TOTAL RETURNS
(For the periods ended December 31, 2013)

Average Annual Total Returns	Inception Date	1-Year	5-Year	10-Year	Since Inception
Service and Premier Shares NORTHERN INSTITUTIONAL DIVERSIFIED ASSETS PORTFOLIO Service Shares	Jul. 01, 1998	0.01%	0.04%	1.46%	2.16%

The 7-day yield for Service Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.

[1] Northern Trust Investments, Inc. has contractually agreed to reimburse certain expenses of the Portfolio (including the administration fee, but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses, acquired fund fees and expenses, a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries, expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio's "Other Expenses" exceed 0.10%. This contractual limitation may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Expense Reimbursement

XML

Shares | NORTHERN INSTITUTIONAL TAX-EXEMPT PORTFOLIO

TAX-EXEMPT PORTFOLIO

INVESTMENT OBJECTIVE

The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to provide, to the extent consistent with the preservation of capital and prescribed portfolio standards, a high level of income exempt from regular federal income tax by investing primarily in municipal instruments.

FEES AND EXPENSES OF THE PORTFOLIO

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Portfolio.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (USD $)	Shares NORTHERN INSTITUTIONAL TAX-EXEMPT PORTFOLIO
Shareholder Fees (fees paid directly from your investment)	none

Annual Portfolio Operating Expenses (expenses that you pay each year as
a percentage of the value of your investment)

Annual Fund Operating Expenses		Shares NORTHERN INSTITUTIONAL TAX-EXEMPT PORTFOLIO
Management Fees		0.25%
Other Expenses		0.13%
Administration Fees		0.10%
Service Agent Fees		none
Other Operating Expenses		0.03%
Total Annual Portfolio Operating Expenses		0.38%
Expense Reimbursement	[1]	(0.03%)
Total Annual Portfolio Operating Expenses	[2]	0.35%

EXAMPLE

The following Example is intended to help you compare the cost of investing in the Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)	1 Year	3 Years	5 Years	10 Years
Shares NORTHERN INSTITUTIONAL TAX-EXEMPT PORTFOLIO	36	119	210	477

PRINCIPAL INVESTMENT STRATEGIES

The Portfolio seeks to achieve its objective by investing primarily in high-quality short-term municipal instruments, the interest on which is exempt from regular federal income tax. The high level of income sought by the Portfolio is relative to yields currently available in the tax-exempt marketplace. Municipal instruments may include:

• Fixed, variable and floating rate notes and similar debt instruments;

• Asset-backed securities that are considered municipal instruments (such as trust certificates backed by municipal bonds);

• Tax-exempt commercial paper;

• Municipal bonds, notes, paper or other instruments; and

• Municipal bonds and notes that are guaranteed as to principal and interest or backed by the U.S. government or by its agencies, instrumentalities or sponsored enterprises.

Except in extraordinary circumstances, at least 80% of the Portfolio’s net assets will be invested in debt instruments that pay interest that is exempt from regular federal income tax. Alternative minimum tax (“AMT”) obligations, which pay interest that may be treated as an item of tax preference to shareholders under the federal AMT, will not be deemed to be eligible debt instruments for the purposes of determining whether the Portfolio meets this policy. To the extent that the Portfolio invests in AMT obligations, a limited portion of the Portfolio’s dividends may be subject to federal income tax for shareholders subject to AMT.

The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio.

During extraordinary market conditions and interest rate environments, all or any portion of the Portfolio’s assets may be uninvested or invested in AMT obligations and taxable instruments. Uninvested assets do not generate income. The Portfolio may not achieve its investment objective during this time.

PRINCIPAL RISKS

STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share.

INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher.

GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio.

PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities.

DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities.

INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities.

MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results.

CREDIT (OR DEFAULT) RISK is the risk that the inability or unwillingness of an issuer or guarantor of a fixed-income security, or a counterparty to a repurchase or other transaction, to meet its payment or other financial obligations will adversely affect the value of the Portfolio’s investments and its yield. Changes in the credit rating of a debt security held by the Portfolio could have a similar effect.

PROJECT/INDUSTRIAL DEVELOPMENT BOND RISK is the risk that the Portfolio may be more sensitive to an adverse economic, business or political development if it invests more than 25% of its assets in municipal instruments, the interest upon which is paid solely from revenues of similar projects, or in industrial development bonds.

TAX RISK is the risk that future legislative or administrative changes or court decisions may materially affect the value of municipal instruments or the ability of the Portfolio to pay tax-exempt dividends.

MUNICIPAL MARKET VOLATILITY RISK is the risk that the Portfolio may be adversely affected by the volatile municipal market. The municipal market can be significantly affected by adverse tax, legislative, or political changes and the financial condition of the issuers of municipal securities.

An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.

PORTFOLIO PERFORMANCE

The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Shares from year to year.

The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.

Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.

CALENDAR YEAR TOTAL RETURN (SHARES)*

* For the periods shown in the bar chart above, the highest quarterly return was 0.85% in the third quarter of 2007, and the lowest quarterly return was 0.00% in the fourth quarter of 2013.

AVERAGE ANNUAL TOTAL RETURNS
(For the periods ended December 31, 2013)

Average Annual Total Returns	Inception Date	1-Year	5-Year	10-Year	Since Inception
Shares NORTHERN INSTITUTIONAL TAX-EXEMPT PORTFOLIO	Aug. 12, 1983	0.01%	0.07%	1.18%	2.87%

The 7-day yield for Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.

[1] Northern Trust Investments, Inc. has contractually agreed to reimburse certain expenses of the Portfolio (including the administration fee; but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses; acquired fund fees and expenses; a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries; expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio's "Other Expenses" exceed 0.10%. This contractual limitation may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Expense Reimbursement

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	NORTHERN INSTITUTIONAL FUNDS
Prospectus Date	rr_ProspectusDate	Apr. 01, 2014
Shares | NORTHERN INSTITUTIONAL DIVERSIFIED ASSETS PORTFOLIO
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	DIVERSIFIED ASSETS PORTFOLIO
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to maximize current income to the extent consistent with the preservation of capital and maintenance of liquidity by investing exclusively in high quality money market instruments.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE PORTFOLIO
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold Shares of the Portfolio.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Portfolio Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	April 1, 2015
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following Example is intended to help you compare the cost of investing in the Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Portfolio seeks to achieve its objective by investing in a broad range of high-quality, U.S. dollar-denominated government, bank and commercial obligations that are available in the money markets, including: Obligations of U.S. banks (including obligations of foreign branches of such banks); Obligations of foreign commercial banks; Commercial paper and other obligations issued or guaranteed by U.S. and foreign corporations and other issuers; Corporate bonds, notes, paper and other instruments that are of high quality; Asset-backed securities and asset-backed commercial paper; Securities issued or guaranteed as to principal and interest by the U.S. government or by its agencies, instrumentalities or sponsored enterprises and custodial receipts with respect thereto; Securities issued or guaranteed by one or more foreign governments or political subdivisions, agencies or instrumentalities; Repurchase agreements; and Municipal securities issued or guaranteed by state or local governmental bodies. The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio. During extraordinary market conditions and interest rate environments, all or any portion of the Portfolio’s assets may be uninvested and will therefore not generate income. The Portfolio may not achieve its investment objective during this time.
Risk [Heading]	rr_RiskHeading	PRINCIPAL RISKS
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share. INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher. GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio. PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities. DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities. INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities. MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results. CREDIT (OR DEFAULT) RISK is the risk that the inability or unwillingness of an issuer or guarantor of a fixed-income security, or a counterparty to a repurchase or other transaction, to meet its payment or other financial obligations will adversely affect the value of the Portfolio’s investments and its yield. Changes in the credit rating of a debt security held by the Portfolio could have a similar effect. FOREIGN SECURITIES RISK is the risk that a foreign security, even if it is a U.S. dollar-denominated foreign security, could lose value as a result of political, financial and economic events in foreign countries, less stringent foreign securities regulations and accounting and disclosure standards or other factors. An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Lose Money [Text]	rr_RiskLoseMoney	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Money Market Fund [Text]	rr_RiskMoneyMarketFund	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	PORTFOLIO PERFORMANCE
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Shares from year to year. The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future. Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Shares from year to year.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800-637-1380
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	www.northerninstitutionalfunds.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	CALENDAR YEAR TOTAL RETURN (SHARES)*
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	* For the periods shown in the bar chart above, the highest quarterly return was 1.27% in the third quarter of 2007, and the lowest quarterly return was 0.00% in the fourth quarter of 2013.
Performance Table Heading	rr_PerformanceTableHeading	AVERAGE ANNUAL TOTAL RETURNS (For the periods ended December 31, 2013)
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	The 7-day yield for Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.
Money Market Seven Day Yield Phone	rr_MoneyMarketSevenDayYieldPhone	800-637-1380
Shares | NORTHERN INSTITUTIONAL DIVERSIFIED ASSETS PORTFOLIO | Shares
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fees	rr_ManagementFeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.12%
Administration Fees	rr_Component1OtherExpensesOverAssets	0.10%
Service Agent Fees	rr_Component2OtherExpensesOverAssets	none
Other Operating Expenses	rr_Component3OtherExpensesOverAssets	0.02%
Total Annual Portfolio Operating Expenses	rr_ExpensesOverAssets	0.37%
Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.02%)	[1]
Total Annual Portfolio Operating Expenses	rr_NetExpensesOverAssets	0.35%	[2]
1 Year	rr_ExpenseExampleYear01	36
3 Years	rr_ExpenseExampleYear03	117
5 Years	rr_ExpenseExampleYear05	206
10 Years	rr_ExpenseExampleYear10	$ 466
2004	rr_AnnualReturn2004	1.08%
2005	rr_AnnualReturn2005	2.96%
2006	rr_AnnualReturn2006	4.79%
2007	rr_AnnualReturn2007	5.03%
2008	rr_AnnualReturn2008	2.08%
2009	rr_AnnualReturn2009	0.22%
2010	rr_AnnualReturn2010	0.02%
2011	rr_AnnualReturn2011	0.03%
2012	rr_AnnualReturn2012	0.01%
2013	rr_AnnualReturn2013	0.01%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2007
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	1.27%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2013
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	0.00%
1-Year	rr_AverageAnnualReturnYear01	0.01%
5-Year	rr_AverageAnnualReturnYear05	0.06%
10-Year	rr_AverageAnnualReturnYear10	1.61%
Since Inception	rr_AverageAnnualReturnSinceInception	4.39%
Inception Date	rr_AverageAnnualReturnInceptionDate	Jun. 01, 1983
Money Market Seven Day Yield, Caption [Text]	rr_MoneyMarketSevenDayYieldCaption	The 7-day yield for Shares of the Portfolio as of December 31, 2013:
Money Market Seven Day Yield	rr_MoneyMarketSevenDayYield	0.01%

[1] Northern Trust Investments, Inc. has contractually agreed to reimburse certain expenses of the Portfolio (including the administration fee; but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses; acquired fund fees and expenses; a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries; expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds; and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio's "Other Expenses" exceed 0.10%. This contractual limitation may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Expense Reimbursement

XML

Service and Premier Shares | NORTHERN INSTITUTIONAL TAX-EXEMPT PORTFOLIO

TAX-EXEMPT PORTFOLIO

INVESTMENT OBJECTIVE

The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to provide, to the extent consistent with the preservation of capital and prescribed portfolio standards, a high level of income exempt from regular federal income tax by investing primarily in municipal instruments.

FEES AND EXPENSES OF THE PORTFOLIO

This table describes the fees and expenses that you may pay if you buy and hold Service and Premier Shares of the Portfolio.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees Service and Premier Shares NORTHERN INSTITUTIONAL TAX-EXEMPT PORTFOLIO (USD $)	Service Shares	Premier Shares
Shareholder Fees (fees paid directly from your investment)	none	none

Annual Portfolio Operating Expenses (expenses that you pay each year as
a percentage of the value of your investment)

Annual Fund Operating Expenses Service and Premier Shares NORTHERN INSTITUTIONAL TAX-EXEMPT PORTFOLIO		Service Shares	Premier Shares
Management Fees		0.25%	0.25%
Other Expenses		0.39%	0.65%
Administration Fees		0.10%	0.10%
Service Agent Fees		0.25%	0.50%
Other Operating Expenses		0.04%	0.05%
Total Annual Portfolio Operating Expenses		0.64%	0.90%
Expense Reimbursement	[1]	(0.03%)	(0.03%)
Total Annual Portfolio Operating Expenses	[2]	0.61%	0.87%

EXAMPLE

The following Example is intended to help you compare the cost of investing in the Service and Premier Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Service and Premier Shares NORTHERN INSTITUTIONAL TAX-EXEMPT PORTFOLIO (USD $)	1 Year	3 Years	5 Years	10 Years
Service Shares	62	202	354	796
Premier Shares	89	284	496	1,105

PRINCIPAL INVESTMENT STRATEGIES

The Portfolio seeks to achieve its objective by investing primarily in high quality short-term municipal instruments, the interest on which is exempt from regular federal income tax. The high level of income sought by the Portfolio is relative to yields currently available in the tax-exempt marketplace. Municipal instruments may include:

• Fixed, variable and floating rate notes and similar debt instruments;

• Asset-backed securities that are considered municipal instruments (such as trust certificates backed by municipal bonds);

• Tax-exempt commercial paper;

• Municipal bonds, notes, paper or other instruments; and

• Municipal bonds and notes that are guaranteed as to principal and interest or backed by the U.S. government or by its agencies, instrumentalities or sponsored enterprises.

Except in extraordinary circumstances, at least 80% of the Portfolio’s net assets will be invested in debt instruments that pay interest that is exempt from regular federal income tax. Alternative minimum tax (“AMT”) obligations, which pay interest that may be treated as an item of tax preference to shareholders under the federal AMT, will not be deemed to be eligible debt instruments for the purposes of determining whether the Portfolio meets this policy. To the extent that the Portfolio invests in AMT obligations, a limited portion of the Portfolio’s dividends may be subject to federal income tax for shareholders subject to AMT.

The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio.

During extraordinary market conditions and interest rate environments, all or any portion of the Portfolio’s assets may be uninvested or invested in taxable instruments. Uninvested assets do not generate income. The Portfolio may not achieve its investment objective during this time.

PRINCIPAL RISKS

STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share.

INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher.

GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio.

PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities.

DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities.

INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities.

MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results.

CREDIT (OR DEFAULT) RISK is the risk that the inability or unwillingness of an issuer or guarantor of a fixed-income security, or a counterparty to a repurchase or other transaction, to meet its payment or other financial obligations will adversely affect the value of the Portfolio’s investments and its yield. Changes in the credit rating of a debt security held by the Portfolio could have a similar effect.

PROJECT/INDUSTRIAL DEVELOPMENT BOND RISK is the risk that the Portfolio may be more sensitive to an adverse economic, business or political development if it invests more than 25% of its assets in municipal instruments, the interest upon which is paid solely from revenues of similar projects, or in industrial development bonds.

TAX RISK is the risk that future legislative or administrative changes or court decisions may materially affect the value of municipal instruments or the ability of the Portfolio to pay tax-exempt dividends.

MUNICIPAL MARKET VOLATILITY RISK is the risk that the Portfolio may be adversely affected by the volatile municipal market. The municipal market can be significantly affected by adverse tax, legislative, or political changes and the financial condition of the issuers of municipal securities.

An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.

PORTFOLIO PERFORMANCE

The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Service Shares from year to year. There are no Premier Shares currently outstanding for the Portfolio.

The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.

Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.

CALENDAR YEAR TOTAL RETURN (SERVICE SHARES)*

* For the periods shown in the bar chart above, the highest quarterly return was 0.79% in the second quarter of 2007, and the lowest quarterly return was 0.00% in the fourth quarter of 2013.

AVERAGE ANNUAL TOTAL RETURNS
(For the periods ended December 31, 2013)

Average Annual Total Returns	Inception Date	1-Year	5-Year	10-Year	Since Inception
Service and Premier Shares NORTHERN INSTITUTIONAL TAX-EXEMPT PORTFOLIO Service Shares	May 13, 1999	0.01%	0.04%	1.03%	1.33%

The 7-day yield for Service Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.

[1] Northern Trust Investments, Inc. has contractually agreed to reimburse certain expenses of the Portfolio (including the administration fee, but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses, acquired fund fees and expenses, a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries, expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio's "Other Expenses" exceed 0.10%. This contractual limitation may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Expense Reimbursement

XML

Shares | NORTHERN INSTITUTIONAL DIVERSIFIED ASSETS PORTFOLIO

DIVERSIFIED ASSETS PORTFOLIO

INVESTMENT OBJECTIVE

The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to maximize current income to the extent consistent with the preservation of capital and maintenance of liquidity by investing exclusively in high quality money market instruments.

FEES AND EXPENSES OF THE PORTFOLIO

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Portfolio.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (USD $)	Shares NORTHERN INSTITUTIONAL DIVERSIFIED ASSETS PORTFOLIO
Shareholder Fees (fees paid directly from your investment)	none

Annual Portfolio Operating Expenses (expenses that you pay each year as
a percentage of the value of your investment)

Annual Fund Operating Expenses		Shares NORTHERN INSTITUTIONAL DIVERSIFIED ASSETS PORTFOLIO
Management Fees		0.25%
Other Expenses		0.12%
Administration Fees		0.10%
Service Agent Fees		none
Other Operating Expenses		0.02%
Total Annual Portfolio Operating Expenses		0.37%
Expense Reimbursement	[1]	(0.02%)
Total Annual Portfolio Operating Expenses	[2]	0.35%

EXAMPLE

The following Example is intended to help you compare the cost of investing in the Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)	1 Year	3 Years	5 Years	10 Years
Shares NORTHERN INSTITUTIONAL DIVERSIFIED ASSETS PORTFOLIO	36	117	206	466

PRINCIPAL INVESTMENT STRATEGIES

The Portfolio seeks to achieve its objective by investing in a broad range of high-quality, U.S. dollar-denominated government, bank and commercial obligations that are available in the money markets, including:

• Obligations of U.S. banks (including obligations of foreign branches of such banks);

• Obligations of foreign commercial banks;

• Commercial paper and other obligations issued or guaranteed by U.S. and foreign corporations and other issuers;

• Corporate bonds, notes, paper and other instruments that are of high quality;

• Asset-backed securities and asset-backed commercial paper;

• Securities issued or guaranteed as to principal and interest by the U.S. government or by its agencies, instrumentalities or sponsored enterprises and custodial receipts with respect thereto;

• Securities issued or guaranteed by one or more foreign governments or political subdivisions, agencies or instrumentalities;

• Repurchase agreements; and

• Municipal securities issued or guaranteed by state or local governmental bodies.

The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio.

During extraordinary market conditions and interest rate environments, all or any portion of the Portfolio’s assets may be uninvested and will therefore not generate income. The Portfolio may not achieve its investment objective during this time.

PRINCIPAL RISKS

STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share.

INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher.

GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio.

PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities.

DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities.

INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities.

MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results.

CREDIT (OR DEFAULT) RISK is the risk that the inability or unwillingness of an issuer or guarantor of a fixed-income security, or a counterparty to a repurchase or other transaction, to meet its payment or other financial obligations will adversely affect the value of the Portfolio’s investments and its yield. Changes in the credit rating of a debt security held by the Portfolio could have a similar effect.

FOREIGN SECURITIES RISK is the risk that a foreign security, even if it is a U.S. dollar-denominated foreign security, could lose value as a result of political, financial and economic events in foreign countries, less stringent foreign securities regulations and accounting and disclosure standards or other factors.

An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.

PORTFOLIO PERFORMANCE

The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Shares from year to year.

The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.

Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.

CALENDAR YEAR TOTAL RETURN (SHARES)*

* For the periods shown in the bar chart above, the highest quarterly return was 1.27% in the third quarter of 2007, and the lowest quarterly return was 0.00% in the fourth quarter of 2013.

AVERAGE ANNUAL TOTAL RETURNS
(For the periods ended December 31, 2013)

Average Annual Total Returns	Inception Date	1-Year	5-Year	10-Year	Since Inception
Shares NORTHERN INSTITUTIONAL DIVERSIFIED ASSETS PORTFOLIO	Jun. 01, 1983	0.01%	0.06%	1.61%	4.39%

The 7-day yield for Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.

[1] Northern Trust Investments, Inc. has contractually agreed to reimburse certain expenses of the Portfolio (including the administration fee; but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses; acquired fund fees and expenses; a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries; expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds; and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio's "Other Expenses" exceed 0.10%. This contractual limitation may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Expense Reimbursement

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	NORTHERN INSTITUTIONAL FUNDS
Prospectus Date	rr_ProspectusDate	Apr. 01, 2014
GFS Shares | NORTHERN INSTITUTIONAL PRIME OBLIGATIONS PORTFOLIO
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	PRIME OBLIGATIONS PORTFOLIO
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to maximize current income to the extent consistent with the preservation of capital and maintenance of liquidity by investing exclusively in high quality money market instruments.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE PORTFOLIO
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold shares of the Portfolio.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Portfolio Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	April 1, 2015
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following Example is intended to help you compare the cost of investing in shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Portfolio seeks to achieve its objective by investing in a broad range of high-quality, U.S. dollar-denominated government, bank and commercial obligations that are available in the money markets, including: Obligations of U.S. banks (including obligations of foreign branches of such banks); Obligations of foreign commercial banks; Commercial paper and other obligations issued or guaranteed by U.S. and foreign corporations and other issuers; Corporate bonds, notes, paper and other instruments that are of high quality; Asset-backed securities and asset-backed commercial paper; Securities issued or guaranteed as to principal and interest by the U.S. government or by its agencies, instrumentalities or sponsored enterprises and custodial receipts with respect thereto; Securities issued or guaranteed by one or more foreign governments or political subdivisions, agencies or instrumentalities; Repurchase agreements; and Municipal securities issued or guaranteed by state or local governmental bodies. The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio. During extraordinary market conditions and interest rate environments, all or any portion of the Portfolio’s assets may be uninvested and will therefore not generate income. The Portfolio may not achieve its investment objective during this time.
Risk [Heading]	rr_RiskHeading	PRINCIPAL RISKS
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share. INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher. CREDIT (OR DEFAULT) RISK is the risk that the inability or unwillingness of an issuer or guarantor of a fixed-income security, or a counterparty to a repurchase or other transaction, to meet its payment or other financial obligations will adversely affect the value of the Portfolio’s investments and its yield. Changes in the credit rating of a debt security held by the Portfolio could have a similar effect. GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio. INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities. MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results. PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities. DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities. FOREIGN SECURITIES RISK is the risk that a foreign security, even if it is a U.S. dollar-denominated foreign security, could lose value as a result of political, financial and economic events in foreign countries, less stringent foreign securities regulations and accounting and disclosure standards or other factors. An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Lose Money [Text]	rr_RiskLoseMoney	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Money Market Fund [Text]	rr_RiskMoneyMarketFund	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	PORTFOLIO PERFORMANCE
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s GFS Shares from year to year. The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future. Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s GFS Shares from year to year.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800-637-1380
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	www.northerninstitutionalfunds.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	CALENDAR YEAR TOTAL RETURN (GFS SHARES)*
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	* For the period shown in the bar chart above, the highest quarterly return was 0.03% in the fourth quarter of 2012, and the lowest quarterly return was 0.00% in the fourth quarter of 2013.
Performance Table Heading	rr_PerformanceTableHeading	AVERAGE ANNUAL TOTAL RETURNS (For the periods ended December 31, 2013)
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	The 7-day yield for GFS Shares of the Portfolio as of December 31, 2013: 0.02%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.
Money Market Seven Day Yield Phone	rr_MoneyMarketSevenDayYieldPhone	800-637-1380
GFS Shares | NORTHERN INSTITUTIONAL PRIME OBLIGATIONS PORTFOLIO | GFS Shares
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fees	rr_ManagementFeesOverAssets	0.15%
Other Expenses	rr_OtherExpensesOverAssets	0.12%
Administration Fees	rr_Component1OtherExpensesOverAssets	0.10%
Service Agent Fees	rr_Component2OtherExpensesOverAssets	none
Other Operating Expenses	rr_Component3OtherExpensesOverAssets	0.02%
Total Annual Portfolio Operating Expenses	rr_ExpensesOverAssets	0.27%
Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.12%)	[1]
Total Annual Portfolio Operating Expenses	rr_NetExpensesOverAssets	0.15%	[2]
1 Year	rr_ExpenseExampleYear01	15
3 Years	rr_ExpenseExampleYear03	75
5 Years	rr_ExpenseExampleYear05	140
10 Years	rr_ExpenseExampleYear10	$ 331
2012	rr_AnnualReturn2012	0.08%
2013	rr_AnnualReturn2013	0.05%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Dec. 31, 2012
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	0.03%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2013
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	0.00%
1-Year	rr_AverageAnnualReturnYear01	0.05%
Since Inception	rr_AverageAnnualReturnSinceInception	0.06%
Inception Date	rr_AverageAnnualReturnInceptionDate	May 10, 2011
Money Market Seven Day Yield, Caption [Text]	rr_MoneyMarketSevenDayYieldCaption	The 7-day yield for GFS Shares of the Portfolio as of December 31, 2013:
Money Market Seven Day Yield	rr_MoneyMarketSevenDayYield	0.02%

[1] Northern Trust Investments, Inc. has contractually agreed to limit the management fees charged to the Portfolio to 0.10% of the Portfolio's average daily net assets; and to reimburse certain expenses of the Portfolio (including the administration fee, but excluding the investment advisory fee and transfer agency fee; servicing fees; extraordinary expenses such as taxes, interest, and indemnification expenses; acquired fund fees and expenses; a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries; expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio's "Other Expenses" exceed 0.05%. These contractual limitations may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc. serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Fee Waiver and Expense Reimbursement

XML

Service and Premier Shares | NORTHERN INSTITUTIONAL TREASURY PORTFOLIO

TREASURY PORTFOLIO

INVESTMENT OBJECTIVE

The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to maximize current income to the extent consistent with the preservation of capital and maintenance of liquidity by investing primarily in U.S. Treasury securities, securities guaranteed as to principal and interest by the U.S. government, and related repurchase agreements.

FEES AND EXPENSES OF THE PORTFOLIO

This table describes the fees and expenses that you may pay if you buy and hold Service and Premier Shares of the Portfolio.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees Service and Premier Shares NORTHERN INSTITUTIONAL TREASURY PORTFOLIO (USD $)	Service Shares	Premier Shares
Shareholder Fees (fees paid directly from your investment)	none	none

Annual Portfolio Operating Expenses (expenses that you pay each year as
a percentage of the value of your investment)

Annual Fund Operating Expenses Service and Premier Shares NORTHERN INSTITUTIONAL TREASURY PORTFOLIO		Service Shares	Premier Shares
Management Fees		0.20%	0.20%
Other Expenses		0.38%	0.64%
Administration Fees		0.10%	0.10%
Service Agent Fees		0.25%	0.50%
Other Operating Expenses		0.03%	0.04%
Total Annual Portfolio Operating Expenses		0.58%	0.84%
Fee Waiver and Expense Reimbursement	[1]	(0.12%)	(0.12%)
Total Annual Portfolio Operating Expenses	[2]	0.46%	0.72%

EXAMPLE

The following Example is intended to help you compare the cost of investing in the Service and Premier Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Service and Premier Shares NORTHERN INSTITUTIONAL TREASURY PORTFOLIO (USD $)	1 Year	3 Years	5 Years	10 Years
Service Shares	47	174	312	714
Premier Shares	74	256	454	1,026

PRINCIPAL INVESTMENT STRATEGIES

The Portfolio seeks to achieve its objective by investing, under normal circumstances, its net assets exclusively in:

• Short-term bills, notes and other obligations issued or guaranteed by the U.S. Treasury (“Treasury Obligations”);

• Repurchase agreements with counterparties collateralized fully by Treasury Obligations; and

• Shares of other money market portfolios of regulated investment companies that i) limit investments to U.S. Treasury Obligations and related repurchase agreements, and ii) determine NAVs based on Rule 2a-7 under the Investment Company Act of 1940, as amended (the “1940 Act”).

The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio.

In addition, during extraordinary market conditions and interest rate environments, all or any portion of the Portfolio’s assets may be uninvested and will therefore not generate income. The Portfolio may not achieve its investment objective during this time.

PRINCIPAL RISKS

STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share.

INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher.

GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio.

PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities.

DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities.

INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities.

MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results.

CREDIT (OR DEFAULT) RISK is the risk that the inability or unwillingness of an issuer or guarantor of a fixed-income security, or a counterparty to a repurchase or other transaction, to meet its payment or other financial obligations will adversely affect the value of the Portfolio’s investments and its yield.

Changes in the credit rating of a debt security held by the Portfolio could have a similar effect.

An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.

PORTFOLIO PERFORMANCE

The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Shares from year to year. There are no Service Shares or Premier Shares currently outstanding for the Portfolio. For this reason, the performance information shown below is only for Shares, which are offered in a separate Prospectus. Service Shares and Premier Shares would have similar annual returns when compared with Shares because Shares, Service Shares and Premier Shares are invested in the same portfolio of securities. The annual returns of Shares would differ from those of Service Shares and Premier Shares only to the extent that the classes do not have the same expenses.

The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.

Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.

CALENDAR YEAR TOTAL RETURN (SHARES)*

* For the periods shown in the bar chart above, the highest quarterly return was 0.05% in the first quarter of 2009, and the lowest quarterly return was 0.00% in the fourth quarter of 2013.

AVERAGE ANNUAL TOTAL RETURNS
(For the periods ended December 31, 2013)

Average Annual Total Returns	Inception Date	1-Year	5-Year	Since Inception
Service and Premier Shares NORTHERN INSTITUTIONAL TREASURY PORTFOLIO Shares	Nov. 05, 2008	0.01%	0.05%	0.05%

The 7-day yield for Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.

[1] Northern Trust Investments, Inc. has contractually agreed to limit the management fees charged to the Portfolio to 0.10% of the Portfolio's average daily net assets and to reimburse certain expenses of the Portfolio (including the administration fee, but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses, acquired fund fees and expenses, a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries, expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio's "Other Expenses" exceed 0.10%. These contractual limitations may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Fee Waiver and Expense Reimbursement

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	NORTHERN INSTITUTIONAL FUNDS
Prospectus Date	rr_ProspectusDate	Apr. 01, 2014
Shares | NORTHERN INSTITUTIONAL U.S. GOVERNMENT SELECT PORTFOLIO
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	U.S. GOVERNMENT SELECT PORTFOLIO
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to maximize current income to the extent consistent with the preservation of capital and maintenance of liquidity by investing exclusively in high quality money market instruments.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE PORTFOLIO
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold Shares of the Portfolio.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Portfolio Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	April 1, 2015
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following Example is intended to help you compare the cost of investing in the Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Portfolio seeks to achieve its objective by investing, under normal circumstances, substantially all (and at least 80%) of its net assets in securities issued or guaranteed as to principal and interest by the U.S. government or by its agencies, instrumentalities or sponsored enterprises. Under normal circumstances, the Portfolio will seek to acquire only those U.S. government securities paying interest that generally is exempt from state income taxation. These securities include obligations issued by the U.S. Treasury and certain U.S. government agencies, instrumentalities or sponsored enterprises, such as the Federal Home Loan Bank and the Federal Farm Credit Banks Funding Corp. The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio. Under unusual circumstances, as when appropriate securities that are exempt from state taxes are unavailable, the Portfolio also may invest in non-exempt U.S. government securities and cash equivalents, including money market funds and repurchase agreements, and hold uninvested cash. Cash assets will not generate income. The Portfolio may not achieve its investment objective during this time. The Portfolio makes significant investments in securities issued by U.S. government-sponsored entities. Such securities are neither issued nor guaranteed by the U.S. Treasury.
Risk [Heading]	rr_RiskHeading	PRINCIPAL RISKS
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share. INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher. GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio. PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities. DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities. INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities. MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results. U.S. GOVERNMENT SECURITIES RISK is the risk that the U.S. government will not provide financial support to its agencies, instrumentalities or sponsored enterprises if it is not obligated to do so by law. Many U.S. government securities purchased by the Portfolio are not backed by the full faith and credit of the United States. It is possible that the issuers of such securities will not have the funds to meet their payment obligations in the future. An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Lose Money [Text]	rr_RiskLoseMoney	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Money Market Fund [Text]	rr_RiskMoneyMarketFund	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	PORTFOLIO PERFORMANCE
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Shares from year to year. The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future. Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Shares from year to year.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800-637-1380
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	www.northerninstitutionalfunds.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	CALENDAR YEAR TOTAL RETURN (SHARES)*
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	* For the periods shown in the bar chart above, the highest quarterly return was 1.27% in the fourth quarter of 2006, and the lowest quarterly return was 0.00% in the fourth quarter of 2013.
Performance Table Heading	rr_PerformanceTableHeading	AVERAGE ANNUAL TOTAL RETURNS (For the periods ended December 31, 2013)
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	The 7-day yield for Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.
Money Market Seven Day Yield Phone	rr_MoneyMarketSevenDayYieldPhone	800-637-1380
Shares | NORTHERN INSTITUTIONAL U.S. GOVERNMENT SELECT PORTFOLIO | Shares
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fees	rr_ManagementFeesOverAssets	0.20%
Other Expenses	rr_OtherExpensesOverAssets	0.12%
Administration Fees	rr_Component1OtherExpensesOverAssets	0.10%
Service Agent Fees	rr_Component2OtherExpensesOverAssets	none
Other Operating Expenses	rr_Component3OtherExpensesOverAssets	0.02%
Total Annual Portfolio Operating Expenses	rr_ExpensesOverAssets	0.32%
Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.12%)	[1]
Total Annual Portfolio Operating Expenses	rr_NetExpensesOverAssets	0.20%	[2]
1 Year	rr_ExpenseExampleYear01	20
3 Years	rr_ExpenseExampleYear03	91
5 Years	rr_ExpenseExampleYear05	168
10 Years	rr_ExpenseExampleYear10	$ 394
2004	rr_AnnualReturn2004	1.15%
2005	rr_AnnualReturn2005	3.02%
2006	rr_AnnualReturn2006	4.82%
2007	rr_AnnualReturn2007	4.96%
2008	rr_AnnualReturn2008	1.99%
2009	rr_AnnualReturn2009	0.14%
2010	rr_AnnualReturn2010	0.03%
2011	rr_AnnualReturn2011	0.01%
2012	rr_AnnualReturn2012	0.01%
2013	rr_AnnualReturn2013	0.01%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Dec. 31, 2006
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	1.27%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2013
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	0.00%
1-Year	rr_AverageAnnualReturnYear01	0.01%
5-Year	rr_AverageAnnualReturnYear05	0.04%
10-Year	rr_AverageAnnualReturnYear10	1.60%
Since Inception	rr_AverageAnnualReturnSinceInception	3.17%
Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 07, 1990
Money Market Seven Day Yield, Caption [Text]	rr_MoneyMarketSevenDayYieldCaption	The 7-day yield for Shares of the Portfolio as of December 31, 2013:
Money Market Seven Day Yield	rr_MoneyMarketSevenDayYield	0.01%

[1] Northern Trust Investments, Inc. has contractually agreed to limit the management fees charged to the Portfolio to 0.10% of the Portfolio's average daily net assets and to reimburse certain expenses of the Portfolio (including the administration fee; but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses; acquired fund fees and expenses; a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries; expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio's "Other Expenses" exceed 0.10%. These contractual limitations may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Fee Waiver and Expense Reimbursement

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	NORTHERN INSTITUTIONAL FUNDS
Prospectus Date	rr_ProspectusDate	Apr. 01, 2014
Shares | NORTHERN INSTITUTIONAL TAX-EXEMPT PORTFOLIO
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	TAX-EXEMPT PORTFOLIO
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to provide, to the extent consistent with the preservation of capital and prescribed portfolio standards, a high level of income exempt from regular federal income tax by investing primarily in municipal instruments.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE PORTFOLIO
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold Shares of the Portfolio.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Portfolio Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	April 1, 2015
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following Example is intended to help you compare the cost of investing in the Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Portfolio seeks to achieve its objective by investing primarily in high-quality short-term municipal instruments, the interest on which is exempt from regular federal income tax. The high level of income sought by the Portfolio is relative to yields currently available in the tax-exempt marketplace. Municipal instruments may include: Fixed, variable and floating rate notes and similar debt instruments; Asset-backed securities that are considered municipal instruments (such as trust certificates backed by municipal bonds); Tax-exempt commercial paper; Municipal bonds, notes, paper or other instruments; and Municipal bonds and notes that are guaranteed as to principal and interest or backed by the U.S. government or by its agencies, instrumentalities or sponsored enterprises. Except in extraordinary circumstances, at least 80% of the Portfolio’s net assets will be invested in debt instruments that pay interest that is exempt from regular federal income tax. Alternative minimum tax (“AMT”) obligations, which pay interest that may be treated as an item of tax preference to shareholders under the federal AMT, will not be deemed to be eligible debt instruments for the purposes of determining whether the Portfolio meets this policy. To the extent that the Portfolio invests in AMT obligations, a limited portion of the Portfolio’s dividends may be subject to federal income tax for shareholders subject to AMT. The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio. During extraordinary market conditions and interest rate environments, all or any portion of the Portfolio’s assets may be uninvested or invested in AMT obligations and taxable instruments. Uninvested assets do not generate income. The Portfolio may not achieve its investment objective during this time.
Risk [Heading]	rr_RiskHeading	PRINCIPAL RISKS
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share. INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher. GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio. PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities. DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities. INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities. MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results. CREDIT (OR DEFAULT) RISK is the risk that the inability or unwillingness of an issuer or guarantor of a fixed-income security, or a counterparty to a repurchase or other transaction, to meet its payment or other financial obligations will adversely affect the value of the Portfolio’s investments and its yield. Changes in the credit rating of a debt security held by the Portfolio could have a similar effect. PROJECT/INDUSTRIAL DEVELOPMENT BOND RISK is the risk that the Portfolio may be more sensitive to an adverse economic, business or political development if it invests more than 25% of its assets in municipal instruments, the interest upon which is paid solely from revenues of similar projects, or in industrial development bonds. TAX RISK is the risk that future legislative or administrative changes or court decisions may materially affect the value of municipal instruments or the ability of the Portfolio to pay tax-exempt dividends. MUNICIPAL MARKET VOLATILITY RISK is the risk that the Portfolio may be adversely affected by the volatile municipal market. The municipal market can be significantly affected by adverse tax, legislative, or political changes and the financial condition of the issuers of municipal securities. An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Lose Money [Text]	rr_RiskLoseMoney	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Money Market Fund [Text]	rr_RiskMoneyMarketFund	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	PORTFOLIO PERFORMANCE
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Shares from year to year. The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future. Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Shares from year to year.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800-637-1380
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	www.northerninstitutionalfunds.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	CALENDAR YEAR TOTAL RETURN (SHARES)*
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	* For the periods shown in the bar chart above, the highest quarterly return was 0.85% in the third quarter of 2007, and the lowest quarterly return was 0.00% in the fourth quarter of 2013.
Performance Table Heading	rr_PerformanceTableHeading	AVERAGE ANNUAL TOTAL RETURNS (For the periods ended December 31, 2013)
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	The 7-day yield for Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.
Money Market Seven Day Yield Phone	rr_MoneyMarketSevenDayYieldPhone	800-637-1380
Shares | NORTHERN INSTITUTIONAL TAX-EXEMPT PORTFOLIO | Shares
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fees	rr_ManagementFeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.13%
Administration Fees	rr_Component1OtherExpensesOverAssets	0.10%
Service Agent Fees	rr_Component2OtherExpensesOverAssets	none
Other Operating Expenses	rr_Component3OtherExpensesOverAssets	0.03%
Total Annual Portfolio Operating Expenses	rr_ExpensesOverAssets	0.38%
Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.03%)	[1]
Total Annual Portfolio Operating Expenses	rr_NetExpensesOverAssets	0.35%	[2]
1 Year	rr_ExpenseExampleYear01	36
3 Years	rr_ExpenseExampleYear03	119
5 Years	rr_ExpenseExampleYear05	210
10 Years	rr_ExpenseExampleYear10	$ 477
2004	rr_AnnualReturn2004	0.91%
2005	rr_AnnualReturn2005	2.11%
2006	rr_AnnualReturn2006	3.15%
2007	rr_AnnualReturn2007	3.34%
2008	rr_AnnualReturn2008	1.99%
2009	rr_AnnualReturn2009	0.28%
2010	rr_AnnualReturn2010	0.03%
2011	rr_AnnualReturn2011	0.02%
2012	rr_AnnualReturn2012	0.01%
2013	rr_AnnualReturn2013	0.01%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2007
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	0.85%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2013
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	0.00%
1-Year	rr_AverageAnnualReturnYear01	0.01%
5-Year	rr_AverageAnnualReturnYear05	0.07%
10-Year	rr_AverageAnnualReturnYear10	1.18%
Since Inception	rr_AverageAnnualReturnSinceInception	2.87%
Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 12, 1983
Money Market Seven Day Yield, Caption [Text]	rr_MoneyMarketSevenDayYieldCaption	The 7-day yield for Shares of the Portfolio as of December 31, 2013:
Money Market Seven Day Yield	rr_MoneyMarketSevenDayYield	0.01%

[1] Northern Trust Investments, Inc. has contractually agreed to reimburse certain expenses of the Portfolio (including the administration fee; but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses; acquired fund fees and expenses; a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries; expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio's "Other Expenses" exceed 0.10%. This contractual limitation may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Expense Reimbursement

XML

GFS Shares | NORTHERN INSTITUTIONAL PRIME OBLIGATIONS PORTFOLIO

PRIME OBLIGATIONS PORTFOLIO

INVESTMENT OBJECTIVE

The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to maximize current income to the extent consistent with the preservation of capital and maintenance of liquidity by investing exclusively in high quality money market instruments.

FEES AND EXPENSES OF THE PORTFOLIO

This table describes the fees and expenses that you may pay if you buy and hold shares of the Portfolio.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (USD $)	GFS Shares NORTHERN INSTITUTIONAL PRIME OBLIGATIONS PORTFOLIO
Shareholder Fees (fees paid directly from your investment)	none

Annual Portfolio Operating Expenses (expenses that you pay each year as
a percentage of the value of your investment)

Annual Fund Operating Expenses		GFS Shares NORTHERN INSTITUTIONAL PRIME OBLIGATIONS PORTFOLIO
Management Fees		0.15%
Other Expenses		0.12%
Administration Fees		0.10%
Service Agent Fees		none
Other Operating Expenses		0.02%
Total Annual Portfolio Operating Expenses		0.27%
Fee Waiver and Expense Reimbursement	[1]	(0.12%)
Total Annual Portfolio Operating Expenses	[2]	0.15%

EXAMPLE

The following Example is intended to help you compare the cost of investing in shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same.

Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)	1 Year	3 Years	5 Years	10 Years
GFS Shares NORTHERN INSTITUTIONAL PRIME OBLIGATIONS PORTFOLIO	15	75	140	331

PRINCIPAL INVESTMENT STRATEGIES

The Portfolio seeks to achieve its objective by investing in a broad range of high-quality, U.S. dollar-denominated government, bank and commercial obligations that are available in the money markets, including:

• Obligations of U.S. banks (including obligations of foreign branches of such banks);

• Obligations of foreign commercial banks;

• Commercial paper and other obligations issued or guaranteed by U.S. and foreign corporations and other issuers;

• Corporate bonds, notes, paper and other instruments that are of high quality;

• Asset-backed securities and asset-backed commercial paper;

• Securities issued or guaranteed as to principal and interest by the U.S. government or by its agencies, instrumentalities or sponsored enterprises and custodial receipts with respect thereto;

• Securities issued or guaranteed by one or more foreign governments or political subdivisions, agencies or instrumentalities;

• Repurchase agreements; and

• Municipal securities issued or guaranteed by state or local governmental bodies.

The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio.

During extraordinary market conditions and interest rate environments, all or any portion of the Portfolio’s assets may be uninvested and will therefore not generate income. The Portfolio may not achieve its investment objective during this time.

PRINCIPAL RISKS

STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share.

INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher.

CREDIT (OR DEFAULT) RISK is the risk that the inability or unwillingness of an issuer or guarantor of a fixed-income security, or a counterparty to a repurchase or other transaction, to meet its payment or other financial obligations will adversely affect the value of the Portfolio’s investments and its yield. Changes in the credit rating of a debt security held by the Portfolio could have a similar effect.

GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio.

INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities.

MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results.

PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities.

DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities.

FOREIGN SECURITIES RISK is the risk that a foreign security, even if it is a U.S. dollar-denominated foreign security, could lose value as a result of political, financial and economic events in foreign countries, less stringent foreign securities regulations and accounting and disclosure standards or other factors.

An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.

PORTFOLIO PERFORMANCE

The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s GFS Shares from year to year.

The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.

Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.

CALENDAR YEAR TOTAL RETURN (GFS SHARES)*

* For the period shown in the bar chart above, the highest quarterly return was 0.03% in the fourth quarter of 2012, and the lowest quarterly return was 0.00% in the fourth quarter of 2013.

AVERAGE ANNUAL TOTAL RETURNS
(For the periods ended December 31, 2013)

Average Annual Total Returns	Inception Date	1-Year	Since Inception
GFS Shares NORTHERN INSTITUTIONAL PRIME OBLIGATIONS PORTFOLIO	May 10, 2011	0.05%	0.06%

The 7-day yield for GFS Shares of the Portfolio as of December 31, 2013: 0.02%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.

[1] Northern Trust Investments, Inc. has contractually agreed to limit the management fees charged to the Portfolio to 0.10% of the Portfolio's average daily net assets; and to reimburse certain expenses of the Portfolio (including the administration fee, but excluding the investment advisory fee and transfer agency fee; servicing fees; extraordinary expenses such as taxes, interest, and indemnification expenses; acquired fund fees and expenses; a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries; expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio's "Other Expenses" exceed 0.05%. These contractual limitations may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc. serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Fee Waiver and Expense Reimbursement

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Document Type	dei_DocumentType	485BPOS
Document Period End Date	dei_DocumentPeriodEndDate	Nov. 30, 2013
Registrant Name	dei_EntityRegistrantName	NORTHERN INSTITUTIONAL FUNDS
Central Index Key	dei_EntityCentralIndexKey	0000710124
Amendment Flag	dei_AmendmentFlag	false
Document Creation Date	dei_DocumentCreationDate	Mar. 21, 2014
Document Effective Date	dei_DocumentEffectiveDate	Apr. 01, 2014
Prospectus Date	rr_ProspectusDate	Apr. 01, 2014

XML

Shares | NORTHERN INSTITUTIONAL TREASURY PORTFOLIO

TREASURY PORTFOLIO

INVESTMENT OBJECTIVE

The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to maximize current income to the extent consistent with the preservation of capital and maintenance of liquidity by investing primarily in U.S. Treasury securities, securities guaranteed as to principal and interest by the U.S. government, and related repurchase agreements.

FEES AND EXPENSES OF THE PORTFOLIO

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Portfolio.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (USD $)	Shares NORTHERN INSTITUTIONAL TREASURY PORTFOLIO
Shareholder Fees (fees paid directly from your investment)	none

Annual Portfolio Operating Expenses (expenses that you pay each year as
a percentage of the value of your investment)

Annual Fund Operating Expenses		Shares NORTHERN INSTITUTIONAL TREASURY PORTFOLIO
Management Fees		0.20%
Other Expenses		0.12%
Administration Fees		0.10%
Service Agent Fees		none
Other Operating Expenses		0.02%
Total Annual Portfolio Operating Expenses		0.32%
Fee Waiver and Expense Reimbursement	[1]	(0.12%)
Total Annual Portfolio Operating Expenses	[2]	0.20%

EXAMPLE

The following Example is intended to help you compare the cost of investing in the Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)	1 Year	3 Years	5 Years	10 Years
Shares NORTHERN INSTITUTIONAL TREASURY PORTFOLIO	20	91	168	394

PRINCIPAL INVESTMENT STRATEGIES

The Portfolio seeks to achieve its objective by investing, under normal circumstances, its net assets exclusively in:

• Short-term bills, notes and other obligations issued or guaranteed by the U.S. Treasury (“Treasury Obligations”);

• Repurchase agreements with counterparties collateralized fully by Treasury Obligations; and

• Shares of other money market portfolios of regulated investment companies that i) limit investments to U.S. Treasury Obligations and related repurchase agreements, and ii) determine NAVs based on Rule 2a-7 under the Investment Company Act of 1940, as amended (the “1940 Act”).

The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio.

In addition, during extraordinary market conditions and interest rate environments, all or any portion of the Portfolio’s assets may be uninvested and will therefore not generate income. The Portfolio may not achieve its investment objective during this time.

PRINCIPAL RISKS

STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share.

INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher.

GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio.

PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities.

DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities.

INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities.

MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results.

CREDIT (OR DEFAULT) RISK is the risk that the inability or unwillingness of an issuer or guarantor of a fixed-income security, or a counterparty to a repurchase or other transaction, to meet its payment or other financial obligations will adversely affect the value of the Portfolio’s investments and its yield. Changes in the credit rating of a debt security held by the Portfolio could have a similar effect.

An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.

PORTFOLIO PERFORMANCE

The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Shares from year to year.

The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.

Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.

CALENDAR YEAR TOTAL RETURN (SHARES)*

* For the periods shown in the bar chart above, the highest quarterly return was 0.05% in the first quarter of 2009, and the lowest quarterly return was 0.00% in the fourth quarter of 2013.

AVERAGE ANNUAL TOTAL RETURNS
(For the periods ended December 31, 2013)

Average Annual Total Returns	Inception Date	1-Year	5-Year	Since Inception
Shares NORTHERN INSTITUTIONAL TREASURY PORTFOLIO	Nov. 05, 2008	0.01%	0.05%	0.05%

The 7-day yield for Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.

[1] Northern Trust Investments, Inc. has contractually agreed to limit the management fees charged to the Portfolio to 0.10% of the Portfolio’s average daily net assets and to reimburse certain expenses of the Portfolio (including the administration fee; but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses; acquired fund fees and expenses; a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries; expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio’s “Other Expenses” exceed 0.10%. These contractual limitations may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Fee Waiver and Expense Reimbursement

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	NORTHERN INSTITUTIONAL FUNDS
Prospectus Date	rr_ProspectusDate	Apr. 01, 2014
Shares | NORTHERN INSTITUTIONAL U.S. GOVERNMENT PORTFOLIO
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	U.S. GOVERNMENT PORTFOLIO
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to maximize current income to the extent consistent with the preservation of capital and maintenance of liquidity by investing exclusively in high quality money market instruments.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE PORTFOLIO
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold Shares of the Portfolio.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Portfolio Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	April 1, 2015
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following Example is intended to help you compare the cost of investing in the Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Portfolio seeks to achieve its objective by investing, under normal circumstances, substantially all (and at least 80%) of its net assets in securities issued or guaranteed as to principal and interest by the U.S. government or by its agencies, instrumentalities or sponsored enterprises, and repurchase agreements backed by such securities. The Portfolio makes significant investments in securities issued by U.S. government-sponsored entities. Such securities are neither issued nor guaranteed by the U.S. Treasury. Under unusual circumstances, as when appropriate U.S. government securities and repurchase agreements backed by such securities are unavailable, the Portfolio also may invest in cash equivalents, including money market funds. The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio. During extraordinary market conditions and interest rate environments, all or any portion of the Portfolio’s assets may be uninvested and will therefore not generate income. The Portfolio may not achieve its investment objective during this time.
Risk [Heading]	rr_RiskHeading	PRINCIPAL RISKS
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share. INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher. GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio. PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities. DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities. INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities. MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results. U.S. GOVERNMENT SECURITIES RISK is the risk that the U.S. government will not provide financial support to its agencies, instrumentalities or sponsored enterprises if it is not obligated to do so by law. Many U.S. government securities purchased by the Portfolio are not backed by the full faith and credit of the United States. It is possible that the issuers of such securities will not have the funds to meet their payment obligations in the future. An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Lose Money [Text]	rr_RiskLoseMoney	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Money Market Fund [Text]	rr_RiskMoneyMarketFund	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	PORTFOLIO PERFORMANCE
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Shares from year to year. The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future. Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Shares from year to year.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800-637-1380
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	www.northerninstitutionalfunds.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	CALENDAR YEAR TOTAL RETURN (SHARES)*
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	* For the periods shown in the bar chart above, the highest quarterly return was 1.25% in the fourth quarter of 2006, and the lowest quarterly return was 0.00% in the fourth quarter of 2013.
Performance Table Heading	rr_PerformanceTableHeading	AVERAGE ANNUAL TOTAL RETURNS (For the periods ended December 31, 2013)
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	The 7-day yield for Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.
Money Market Seven Day Yield Phone	rr_MoneyMarketSevenDayYieldPhone	800-637-1380
Shares | NORTHERN INSTITUTIONAL U.S. GOVERNMENT PORTFOLIO | Shares
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fees	rr_ManagementFeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.12%
Administration Fees	rr_Component1OtherExpensesOverAssets	0.10%
Service Agent Fees	rr_Component2OtherExpensesOverAssets	none
Other Operating Expenses	rr_Component3OtherExpensesOverAssets	0.02%
Total Annual Portfolio Operating Expenses	rr_ExpensesOverAssets	0.37%
Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.02%)	[1]
Total Annual Portfolio Operating Expenses	rr_NetExpensesOverAssets	0.35%	[2]
1 Year	rr_ExpenseExampleYear01	36
3 Years	rr_ExpenseExampleYear03	117
5 Years	rr_ExpenseExampleYear05	206
10 Years	rr_ExpenseExampleYear10	$ 466
2004	rr_AnnualReturn2004	1.06%
2005	rr_AnnualReturn2005	2.92%
2006	rr_AnnualReturn2006	4.74%
2007	rr_AnnualReturn2007	4.87%
2008	rr_AnnualReturn2008	2.00%
2009	rr_AnnualReturn2009	0.07%
2010	rr_AnnualReturn2010	0.02%
2011	rr_AnnualReturn2011	0.02%
2012	rr_AnnualReturn2012	0.01%
2013	rr_AnnualReturn2013	0.01%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Dec. 31, 2006
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	1.25%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2013
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	0.00%
1-Year	rr_AverageAnnualReturnYear01	0.01%
5-Year	rr_AverageAnnualReturnYear05	0.03%
10-Year	rr_AverageAnnualReturnYear10	1.55%
Since Inception	rr_AverageAnnualReturnSinceInception	3.86%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 29, 1985
Money Market Seven Day Yield, Caption [Text]	rr_MoneyMarketSevenDayYieldCaption	The 7-day yield for Shares of the Portfolio as of December 31, 2013:
Money Market Seven Day Yield	rr_MoneyMarketSevenDayYield	0.01%

[1] Northern Trust Investments, Inc. has contractually agreed to reimburse certain expenses of the Portfolio (including the administration fee; but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses; acquired fund fees and expenses; a portion of the compensation paid to each Trustee who is not an officer; director or employee of Northern Trust Corporation or its subsidiaries; expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds; and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio’s “Other Expenses” exceed 0.10%. This contractual limitation may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Expense Reimbursement

XML

Shares | NORTHERN INSTITUTIONAL U.S. GOVERNMENT SELECT PORTFOLIO

U.S. GOVERNMENT SELECT PORTFOLIO

INVESTMENT OBJECTIVE

The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to maximize current income to the extent consistent with the preservation of capital and maintenance of liquidity by investing exclusively in high quality money market instruments.

FEES AND EXPENSES OF THE PORTFOLIO

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Portfolio.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees (USD $)	Shares NORTHERN INSTITUTIONAL U.S. GOVERNMENT SELECT PORTFOLIO
Shareholder Fees (fees paid directly from your investment)	none

Annual Portfolio Operating Expenses (expenses that you pay each year as
a percentage of the value of your investment)

Annual Fund Operating Expenses		Shares NORTHERN INSTITUTIONAL U.S. GOVERNMENT SELECT PORTFOLIO
Management Fees		0.20%
Other Expenses		0.12%
Administration Fees		0.10%
Service Agent Fees		none
Other Operating Expenses		0.02%
Total Annual Portfolio Operating Expenses		0.32%
Fee Waiver and Expense Reimbursement	[1]	(0.12%)
Total Annual Portfolio Operating Expenses	[2]	0.20%

EXAMPLE

The following Example is intended to help you compare the cost of investing in the Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)	1 Year	3 Years	5 Years	10 Years
Shares NORTHERN INSTITUTIONAL U.S. GOVERNMENT SELECT PORTFOLIO	20	91	168	394

PRINCIPAL INVESTMENT STRATEGIES

The Portfolio seeks to achieve its objective by investing, under normal circumstances, substantially all (and at least 80%) of its net assets in securities issued or guaranteed as to principal and interest by the U.S. government or by its agencies, instrumentalities or sponsored enterprises. Under normal circumstances, the Portfolio will seek to acquire only those U.S. government securities paying interest that generally is exempt from state income taxation. These securities include obligations issued by the U.S. Treasury and certain U.S. government agencies, instrumentalities or sponsored enterprises, such as the Federal Home Loan Bank and the Federal Farm Credit Banks Funding Corp.

The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio.

Under unusual circumstances, as when appropriate securities that are exempt from state taxes are unavailable, the Portfolio also may invest in non-exempt U.S. government securities and cash equivalents, including money market funds and repurchase agreements, and hold uninvested cash. Cash assets will not generate income. The Portfolio may not achieve its investment objective during this time.

The Portfolio makes significant investments in securities issued by U.S. government-sponsored entities. Such securities are neither issued nor guaranteed by the U.S. Treasury.

PRINCIPAL RISKS

STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share.

INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher.

GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio.

PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities.

DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities.

INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities.

MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results.

U.S. GOVERNMENT SECURITIES RISK is the risk that the U.S. government will not provide financial support to its agencies, instrumentalities or sponsored enterprises if it is not obligated to do so by law. Many U.S. government securities purchased by the Portfolio are not backed by the full faith and credit of the United States. It is possible that the issuers of such securities will not have the funds to meet their payment obligations in the future.

An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.

PORTFOLIO PERFORMANCE

The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Shares from year to year. The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.

Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.

CALENDAR YEAR TOTAL RETURN (SHARES)*

* For the periods shown in the bar chart above, the highest quarterly return was 1.27% in the fourth quarter of 2006, and the lowest quarterly return was 0.00% in the fourth quarter of 2013.

AVERAGE ANNUAL TOTAL RETURNS
(For the periods ended December 31, 2013)

Average Annual Total Returns	Inception Date	1-Year	5-Year	10-Year	Since Inception
Shares NORTHERN INSTITUTIONAL U.S. GOVERNMENT SELECT PORTFOLIO	Nov. 07, 1990	0.01%	0.04%	1.60%	3.17%

The 7-day yield for Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.

[1] Northern Trust Investments, Inc. has contractually agreed to limit the management fees charged to the Portfolio to 0.10% of the Portfolio's average daily net assets and to reimburse certain expenses of the Portfolio (including the administration fee; but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses; acquired fund fees and expenses; a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries; expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio's "Other Expenses" exceed 0.10%. These contractual limitations may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Fee Waiver and Expense Reimbursement

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	NORTHERN INSTITUTIONAL FUNDS
Prospectus Date	rr_ProspectusDate	Apr. 01, 2014
Service and Premier Shares | NORTHERN INSTITUTIONAL U.S. GOVERNMENT SELECT PORTFOLIO
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	U.S. GOVERNMENT SELECT PORTFOLIO
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to maximize current income to the extent consistent with the preservation of capital and maintenance of liquidity by investing exclusively in high quality money market instruments.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE PORTFOLIO
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold Service and Premier Shares of the Portfolio.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Portfolio Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	April 1, 2015
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following Example is intended to help you compare the cost of investing in the Service and Premier Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Portfolio seeks to achieve its objective by investing, under normal circumstances, substantially all (and at least 80%) of its net assets in securities issued or guaranteed as to principal and interest by the U.S. government or by its agencies, instrumentalities or sponsored enterprises. Under normal circumstances, the Portfolio will seek to acquire only those U.S. government securities paying interest that generally is exempt from state income taxation. These securities include obligations issued by the U.S. Treasury and certain U.S. government agencies, instrumentalities or sponsored enterprises, such as the Federal Home Loan Bank and the Federal Farm Credit Banks Funding Corp. The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio. Under unusual circumstances, as when appropriate securities that are exempt from state taxes are unavailable, the Portfolio also may invest in non-exempt U.S. government securities and cash equivalents, including money market funds and repurchase agreements, and hold uninvested cash. Cash assets will not generate income. The Portfolio may not achieve its investment objective during this time. The Portfolio makes significant investments in securities issued by U.S. government-sponsored entities. Such securities are neither issued nor guaranteed by the U.S. Treasury.
Risk [Heading]	rr_RiskHeading	PRINCIPAL RISKS
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share. INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher. GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio. PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities. DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities. INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities. MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results. U.S. GOVERNMENT SECURITIES RISK is the risk that the U.S. government will not provide financial support to its agencies, instrumentalities or sponsored enterprises if it is not obligated to do so by law. Many U.S. government securities purchased by the Portfolio are not backed by the full faith and credit of the United States. It is possible that the issuers of such securities will not have the funds to meet their payment obligations in the future. An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Lose Money [Text]	rr_RiskLoseMoney	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Money Market Fund [Text]	rr_RiskMoneyMarketFund	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	PORTFOLIO PERFORMANCE
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Service Shares from year to year. There are no Premier Shares currently outstanding for the Portfolio. The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future. Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Service Shares from year to year.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800-637-1380
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	www.northerninstitutionalfunds.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	CALENDAR YEAR TOTAL RETURN (SERVICE SHARES)*
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	* For the periods shown in the bar chart above, the highest quarterly return was 1.20% in the fourth quarter of 2006, and the lowest quarterly return was 0.00% in the fourth quarter of 2013.
Performance Table Heading	rr_PerformanceTableHeading	AVERAGE ANNUAL TOTAL RETURNS (For the periods ended December 31, 2013)
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	The 7-day yield for Service Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.
Money Market Seven Day Yield Phone	rr_MoneyMarketSevenDayYieldPhone	800-637-1380
Service and Premier Shares | NORTHERN INSTITUTIONAL U.S. GOVERNMENT SELECT PORTFOLIO | Service Shares
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fees	rr_ManagementFeesOverAssets	0.20%
Other Expenses	rr_OtherExpensesOverAssets	0.38%
Administration Fees	rr_Component1OtherExpensesOverAssets	0.10%
Service Agent Fees	rr_Component2OtherExpensesOverAssets	0.25%
Other Operating Expenses	rr_Component3OtherExpensesOverAssets	0.03%
Total Annual Portfolio Operating Expenses	rr_ExpensesOverAssets	0.58%
Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.12%)	[1]
Total Annual Portfolio Operating Expenses	rr_NetExpensesOverAssets	0.46%	[2]
1 Year	rr_ExpenseExampleYear01	47
3 Years	rr_ExpenseExampleYear03	174
5 Years	rr_ExpenseExampleYear05	312
10 Years	rr_ExpenseExampleYear10	714
2004	rr_AnnualReturn2004	0.89%
2005	rr_AnnualReturn2005	2.76%
2006	rr_AnnualReturn2006	4.55%
2007	rr_AnnualReturn2007	4.69%
2008	rr_AnnualReturn2008	1.73%
2009	rr_AnnualReturn2009	0.03%
2010	rr_AnnualReturn2010	0.02%
2011	rr_AnnualReturn2011	0.01%
2012	rr_AnnualReturn2012	0.01%
2013	rr_AnnualReturn2013	0.01%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Dec. 31, 2006
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	1.20%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2013
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	0.00%
1-Year	rr_AverageAnnualReturnYear01	0.01%
5-Year	rr_AverageAnnualReturnYear05	0.02%
10-Year	rr_AverageAnnualReturnYear10	1.45%
Since Inception	rr_AverageAnnualReturnSinceInception	1.98%
Inception Date	rr_AverageAnnualReturnInceptionDate	May 28, 1999
Money Market Seven Day Yield, Caption [Text]	rr_MoneyMarketSevenDayYieldCaption	The 7-day yield for Service Shares of the Portfolio as of December 31, 2013:
Money Market Seven Day Yield	rr_MoneyMarketSevenDayYield	0.01%
Service and Premier Shares | NORTHERN INSTITUTIONAL U.S. GOVERNMENT SELECT PORTFOLIO | Premier Shares
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fees	rr_ManagementFeesOverAssets	0.20%
Other Expenses	rr_OtherExpensesOverAssets	0.64%
Administration Fees	rr_Component1OtherExpensesOverAssets	0.10%
Service Agent Fees	rr_Component2OtherExpensesOverAssets	0.50%
Other Operating Expenses	rr_Component3OtherExpensesOverAssets	0.04%
Total Annual Portfolio Operating Expenses	rr_ExpensesOverAssets	0.84%
Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.12%)	[1]
Total Annual Portfolio Operating Expenses	rr_NetExpensesOverAssets	0.72%	[2]
1 Year	rr_ExpenseExampleYear01	74
3 Years	rr_ExpenseExampleYear03	256
5 Years	rr_ExpenseExampleYear05	454
10 Years	rr_ExpenseExampleYear10	$ 1,026

[1] Northern Trust Investments, Inc. has contractually agreed to limit the management fees charged to the Portfolio to 0.10% of the Portfolio's average daily net assets and to reimburse certain expenses of the Portfolio (including the administration fee, but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses, acquired fund fees and expenses, a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries, expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio's "Other Expenses" exceed 0.10%. These contractual limitations may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Fee Waiver and Expense Reimbursement

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	NORTHERN INSTITUTIONAL FUNDS
Prospectus Date	rr_ProspectusDate	Apr. 01, 2014
Service and Premier Shares | NORTHERN INSTITUTIONAL MUNICIPAL PORTFOLIO
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	MUNICIPAL PORTFOLIO
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to provide, to the extent consistent with the preservation of capital, a high level of income exempt from regular federal income tax by investing primarily in municipal instruments. This objective may be changed without shareholder approval.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE PORTFOLIO
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold Service and Premier Shares of the Portfolio.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Portfolio Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	April 1, 2015
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following Example is intended to help you compare the cost of investing in the Service and Premier Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Portfolio seeks to achieve its objective by investing primarily in high quality short-term municipal instruments, the interest on which is exempt from regular federal income tax. The high level of income sought by the Portfolio is relative to yields currently available in the tax-exempt marketplace. Municipal instruments may include: Fixed, variable and floating rate notes and similar debt instruments; Asset-backed securities that are considered municipal instruments (such as trust certificates backed by municipal bonds); Tax-exempt commercial paper; Municipal bonds, notes, paper or other instruments; and Municipal bonds and notes that are guaranteed as to principal and interest or backed by the U.S. government or by its agencies, instrumentalities or sponsored enterprises. Except in extraordinary circumstances, at least 80% of the Portfolio’s net assets will be invested in debt instruments that pay interest that is exempt from regular federal income tax. Alternative minimum tax (“AMT”) obligations, which pay interest that may be treated as an item of tax preference to shareholders under the federal AMT, will be deemed eligible investments for the purposes of determining whether the portfolio meets this policy. To the extent that the Portfolio invests in AMT obligations, a significant portion of the Portfolio’s dividends may be subject to federal income tax for shareholders subject to AMT. The Portfolio is not limited in the amount of its assets that may be invested in AMT obligations. The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio. During extraordinary market conditions and interest rate environments, all or any portion of the Portfolio’s assets may be held uninvested or invested in taxable instruments. Uninvested assets do not generate income. The Portfolio may not achieve its investment objective during this time.
Risk [Heading]	rr_RiskHeading	PRINCIPAL RISKS
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share. INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher. GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio. PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities. DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities. INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities. MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results. CREDIT (OR DEFAULT) RISK is the risk that the inability or unwillingness of an issuer or guarantor of a fixed-income security, or a counterparty to a repurchase or other transaction, to meet its payment or other financial obligations will adversely affect the value of the Portfolio’s investments and its yield. Changes in the credit rating of a debt security held by the Portfolio could have a similar effect. PROJECT/INDUSTRIAL DEVELOPMENT BOND RISK is the risk that the Portfolio may be more sensitive to an adverse economic, business or political development if it invests more than 25% of its assets in municipal instruments, the interest upon which is paid solely from revenues of similar projects, or in industrial development bonds. TAX RISK is the risk that future legislative or administrative changes or court decisions may materially affect the value of municipal instruments or the ability of the Portfolio to pay tax-exempt dividends. MUNICIPAL MARKET VOLATILITY RISK is the risk that the Portfolio may be adversely affected by the volatile municipal market. The municipal market can be significantly affected by adverse tax, legislative, or political changes and the financial condition of the issuers of municipal securities. An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Lose Money [Text]	rr_RiskLoseMoney	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Money Market Fund [Text]	rr_RiskMoneyMarketFund	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	PORTFOLIO PERFORMANCE
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Service Shares from year to year. There are no Premier Shares currently outstanding for the Portfolio. The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future. Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Service Shares from year to year.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800-637-1380
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	www.northerninstitutionalfunds.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	CALENDAR YEAR TOTAL RETURN (SERVICE SHARES)*
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	* For the periods shown in the bar chart above, the highest quarterly return was 0.83% in the third quarter of 2007, and the lowest quarterly return was 0.00% in the third quarter of 2013.
Performance Table Heading	rr_PerformanceTableHeading	AVERAGE ANNUAL TOTAL RETURNS (For the periods ended December 31, 2013)
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	The 7-day yield for Service Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.
Money Market Seven Day Yield Phone	rr_MoneyMarketSevenDayYieldPhone	800-637-1380
Service and Premier Shares | NORTHERN INSTITUTIONAL MUNICIPAL PORTFOLIO | Service Shares
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fees	rr_ManagementFeesOverAssets	0.20%
Other Expenses	rr_OtherExpensesOverAssets	0.38%
Administration Fees	rr_Component1OtherExpensesOverAssets	0.10%
Service Agent Fees	rr_Component2OtherExpensesOverAssets	0.25%
Other Operating Expenses	rr_Component3OtherExpensesOverAssets	0.03%
Total Annual Portfolio Operating Expenses	rr_ExpensesOverAssets	0.58%
Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.12%)	[1]
Total Annual Portfolio Operating Expenses	rr_NetExpensesOverAssets	0.46%	[2]
1 Year	rr_ExpenseExampleYear01	47
3 Years	rr_ExpenseExampleYear03	174
5 Years	rr_ExpenseExampleYear05	312
10 Years	rr_ExpenseExampleYear10	714
2004	rr_AnnualReturn2004	0.80%
2005	rr_AnnualReturn2005	2.00%
2006	rr_AnnualReturn2006	3.03%
2007	rr_AnnualReturn2007	3.23%
2008	rr_AnnualReturn2008	1.83%
2009	rr_AnnualReturn2009	0.19%
2010	rr_AnnualReturn2010	0.02%
2011	rr_AnnualReturn2011	0.02%
2012	rr_AnnualReturn2012	0.02%
2013	rr_AnnualReturn2013	0.02%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2007
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	0.83%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2013
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	0.00%
1-Year	rr_AverageAnnualReturnYear01	0.02%
5-Year	rr_AverageAnnualReturnYear05	0.05%
10-Year	rr_AverageAnnualReturnYear10	1.11%
Since Inception	rr_AverageAnnualReturnSinceInception	1.34%
Inception Date	rr_AverageAnnualReturnInceptionDate	Feb. 11, 2000
Money Market Seven Day Yield, Caption [Text]	rr_MoneyMarketSevenDayYieldCaption	The 7-day yield for Service Shares of the Portfolio as of December 31, 2013:
Money Market Seven Day Yield	rr_MoneyMarketSevenDayYield	0.01%
Service and Premier Shares | NORTHERN INSTITUTIONAL MUNICIPAL PORTFOLIO | Premier Shares
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fees	rr_ManagementFeesOverAssets	0.20%
Other Expenses	rr_OtherExpensesOverAssets	0.64%
Administration Fees	rr_Component1OtherExpensesOverAssets	0.10%
Service Agent Fees	rr_Component2OtherExpensesOverAssets	0.50%
Other Operating Expenses	rr_Component3OtherExpensesOverAssets	0.04%
Total Annual Portfolio Operating Expenses	rr_ExpensesOverAssets	0.84%
Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.12%)	[1]
Total Annual Portfolio Operating Expenses	rr_NetExpensesOverAssets	0.72%	[2]
1 Year	rr_ExpenseExampleYear01	74
3 Years	rr_ExpenseExampleYear03	256
5 Years	rr_ExpenseExampleYear05	454
10 Years	rr_ExpenseExampleYear10	$ 1,026

[1] Northern Trust Investments, Inc. has contractually agreed to limit the management fees charged to the Portfolio to 0.10% of the Portfolio's average daily net assets and to reimburse certain expenses of the Portfolio (including the administration fee, but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses, acquired fund fees and expenses, a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries, expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio's "Other Expenses" exceed 0.10%. These contractual limitations may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Fee Waiver and Expense Reimbursement

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	NORTHERN INSTITUTIONAL FUNDS
Prospectus Date	rr_ProspectusDate	Apr. 01, 2014
Shares, Service and Premier Shares | NORTHERN INSTITUTIONAL PRIME OBLIGATIONS PORTFOLIO
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	PRIME OBLIGATIONS PORTFOLIO
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to maximize current income to the extent consistent with the preservation of capital and maintenance of liquidity by investing exclusively in high quality money market instruments.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE PORTFOLIO
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold shares of the Portfolio.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Portfolio Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	April 1, 2015
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following Example is intended to help you compare the cost of investing in shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Portfolio seeks to achieve its objective by investing in a broad range of high-quality, U.S. dollar-denominated government, bank and commercial obligations that are available in the money markets, including: Obligations of U.S. banks (including obligations of foreign branches of such banks); Obligations of foreign commercial banks; Commercial paper and other obligations issued or guaranteed by U.S. and foreign corporations and other issuers; Corporate bonds, notes, paper and other instruments that are of high quality; Asset-backed securities and asset-backed commercial paper; Securities issued or guaranteed as to principal and interest by the U.S. government or by its agencies, instrumentalities or sponsored enterprises and custodial receipts with respect thereto; Securities issued or guaranteed by one or more foreign governments or political subdivisions, agencies or instrumentalities; Repurchase agreements; and Municipal securities issued or guaranteed by state or local governmental bodies. The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio. During extraordinary market conditions and interest rate environments, all or any portion of the Portfolio’s assets may be uninvested and will therefore not generate income. The Portfolio may not achieve its investment objective during this time.
Risk [Heading]	rr_RiskHeading	PRINCIPAL RISKS
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share. INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher. CREDIT (OR DEFAULT) RISK is the risk that the inability or unwillingness of an issuer or guarantor of a fixed-income security, or a counterparty to a repurchase or other transaction, to meet its payment or other financial obligations will adversely affect the value of the Portfolio’s investments and its yield. Changes in the credit rating of a debt security held by the Portfolio could have a similar effect. GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio. INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities. MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results. PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities. DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities. FOREIGN SECURITIES RISK is the risk that a foreign security, even if it is a U.S. dollar-denominated foreign security, could lose value as a result of political, financial and economic events in foreign countries, less stringent foreign securities regulations and accounting and disclosure standards or other factors. An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Lose Money [Text]	rr_RiskLoseMoney	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Money Market Fund [Text]	rr_RiskMoneyMarketFund	Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	PORTFOLIO PERFORMANCE
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Shares from year to year. There are no Premier Shares currently outstanding for the Portfolio. The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future. Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Shares from year to year.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800-637-1380
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	www.northerninstitutionalfunds.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	CALENDAR YEAR TOTAL RETURN (SHARES)*
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	*For the periods shown in the bar chart above, the highest quarterly return was 1.31% in the third quarter of 2007, and the lowest quarterly return was 0.00% in the fourth quarter of 2013.
Performance Table Heading	rr_PerformanceTableHeading	AVERAGE ANNUAL TOTAL RETURNS (For the periods ended December 31, 2013)
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	The 7-day yield for Shares of the Portfolio as of December 31, 2013: 0.02%. The 7-day yield for Service Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.
Money Market Seven Day Yield Phone	rr_MoneyMarketSevenDayYieldPhone	800-637-1380
Shares, Service and Premier Shares | NORTHERN INSTITUTIONAL PRIME OBLIGATIONS PORTFOLIO | Shares
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fees	rr_ManagementFeesOverAssets	0.15%
Other Expenses	rr_OtherExpensesOverAssets	0.12%
Administration Fees	rr_Component1OtherExpensesOverAssets	0.10%
Service Agent Fees	rr_Component2OtherExpensesOverAssets	none
Other Operating Expenses	rr_Component3OtherExpensesOverAssets	0.02%
Total Annual Portfolio Operating Expenses	rr_ExpensesOverAssets	0.27%
Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.12%)	[1]
Total Annual Portfolio Operating Expenses	rr_NetExpensesOverAssets	0.15%	[2]
1 Year	rr_ExpenseExampleYear01	15
3 Years	rr_ExpenseExampleYear03	75
5 Years	rr_ExpenseExampleYear05	140
10 Years	rr_ExpenseExampleYear10	331
2004	rr_AnnualReturn2004	1.23%
2005	rr_AnnualReturn2005	3.12%
2006	rr_AnnualReturn2006	4.96%
2007	rr_AnnualReturn2007	5.18%
2008	rr_AnnualReturn2008	2.23%
2009	rr_AnnualReturn2009	0.39%
2010	rr_AnnualReturn2010	0.15%
2011	rr_AnnualReturn2011	0.08%
2012	rr_AnnualReturn2012	0.08%
2013	rr_AnnualReturn2013	0.05%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2007
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	1.31%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2013
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	0.00%
1-Year	rr_AverageAnnualReturnYear01	0.05%
5-Year	rr_AverageAnnualReturnYear05	0.15%
10-Year	rr_AverageAnnualReturnYear10	1.73%
Since Inception	rr_AverageAnnualReturnSinceInception	1.70%
Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 21, 2003
Money Market Seven Day Yield, Caption [Text]	rr_MoneyMarketSevenDayYieldCaption	The 7-day yield for Shares of the Portfolio as of December 31, 2013:
Money Market Seven Day Yield	rr_MoneyMarketSevenDayYield	0.02%
Shares, Service and Premier Shares | NORTHERN INSTITUTIONAL PRIME OBLIGATIONS PORTFOLIO | Service Shares
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fees	rr_ManagementFeesOverAssets	0.15%
Other Expenses	rr_OtherExpensesOverAssets	0.38%
Administration Fees	rr_Component1OtherExpensesOverAssets	0.10%
Service Agent Fees	rr_Component2OtherExpensesOverAssets	0.25%
Other Operating Expenses	rr_Component3OtherExpensesOverAssets	0.03%
Total Annual Portfolio Operating Expenses	rr_ExpensesOverAssets	0.53%
Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.12%)	[1]
Total Annual Portfolio Operating Expenses	rr_NetExpensesOverAssets	0.41%	[2]
1 Year	rr_ExpenseExampleYear01	42
3 Years	rr_ExpenseExampleYear03	158
5 Years	rr_ExpenseExampleYear05	284
10 Years	rr_ExpenseExampleYear10	653
1-Year	rr_AverageAnnualReturnYear01	0.05%
5-Year	rr_AverageAnnualReturnYear05	0.07%
10-Year	rr_AverageAnnualReturnYear10	1.56%
Since Inception	rr_AverageAnnualReturnSinceInception	1.53%
Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 02, 2003
Money Market Seven Day Yield, Caption [Text]	rr_MoneyMarketSevenDayYieldCaption	The 7-day yield for Service Shares of the Portfolio as of December 31, 2013:
Money Market Seven Day Yield	rr_MoneyMarketSevenDayYield	0.01%
Shares, Service and Premier Shares | NORTHERN INSTITUTIONAL PRIME OBLIGATIONS PORTFOLIO | Premier Shares
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fees	rr_ManagementFeesOverAssets	0.15%
Other Expenses	rr_OtherExpensesOverAssets	0.64%
Administration Fees	rr_Component1OtherExpensesOverAssets	0.10%
Service Agent Fees	rr_Component2OtherExpensesOverAssets	0.50%
Other Operating Expenses	rr_Component3OtherExpensesOverAssets	0.04%
Total Annual Portfolio Operating Expenses	rr_ExpensesOverAssets	0.79%
Fee Waiver and Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.12%)	[1]
Total Annual Portfolio Operating Expenses	rr_NetExpensesOverAssets	0.67%	[2]
1 Year	rr_ExpenseExampleYear01	68
3 Years	rr_ExpenseExampleYear03	240
5 Years	rr_ExpenseExampleYear05	427
10 Years	rr_ExpenseExampleYear10	$ 967

[1] Northern Trust Investments, Inc. has contractually agreed to limit the management fees charged to the Portfolio to 0.10% of the Portfolio's average daily net assets and to reimburse certain expenses of the Portfolio (including the administration fee, but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses, acquired fund fees and expenses, a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries, expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio's "Other Expenses" exceed 0.05%. These contractual limitations may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc. serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Fee Waiver and Expense Reimbursement

XML

Service and Premier Shares | NORTHERN INSTITUTIONAL U.S. GOVERNMENT PORTFOLIO

U.S. GOVERNMENT PORTFOLIO

INVESTMENT OBJECTIVE

The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to maximize current income to the extent consistent with the preservation of capital and maintenance of liquidity by investing exclusively in high quality money market instruments.

FEES AND EXPENSES OF THE PORTFOLIO

This table describes the fees and expenses that you may pay if you buy and hold Service and Premier Shares of the Portfolio.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees Service and Premier Shares NORTHERN INSTITUTIONAL U.S. GOVERNMENT PORTFOLIO (USD $)	Service Shares	Premier Shares
Shareholder Fees (fees paid directly from your investment)	none	none

Annual Portfolio Operating Expenses (expenses that you pay each year as
a percentage of the value of your investment)

Annual Fund Operating Expenses Service and Premier Shares NORTHERN INSTITUTIONAL U.S. GOVERNMENT PORTFOLIO		Service Shares	Premier Shares
Management Fees		0.25%	0.25%
Other Expenses		0.38%	0.64%
Administration Fees		0.10%	0.10%
Service Agent Fees		0.25%	0.50%
Other Operating Expenses		0.03%	0.04%
Total Annual Portfolio Operating Expenses		0.63%	0.89%
Expense Reimbursement	[1]	(0.02%)	(0.02%)
Total Annual Portfolio Operating Expenses	[2]	0.61%	0.87%

EXAMPLE

The following Example is intended to help you compare the cost of investing in the Service and Premier Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Service and Premier Shares NORTHERN INSTITUTIONAL U.S. GOVERNMENT PORTFOLIO (USD $)	1 Year	3 Years	5 Years	10 Years
Service Shares	62	200	349	784
Premier Shares	89	282	491	1,094

PRINCIPAL INVESTMENT STRATEGIES

The Portfolio seeks to achieve its objective by investing, under normal circumstances, substantially all (and at least 80%) of its net assets in securities issued or guaranteed as to principal and interest by the U.S. government or by its agencies, instrumentalities or sponsored enterprises, and repurchase agreements backed by such securities.

The Portfolio makes significant investments in securities issued by U.S. government-sponsored entities. Such securities are neither issued nor guaranteed by the U.S. Treasury. Under unusual circumstances, as when appropriate U.S. government securities and repurchase agreements backed by such securities are unavailable, the Portfolio also may invest in cash equivalents, including money market funds.

The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio.

During extraordinary market conditions and interest rate environments, all or any portion of the Portfolio’s assets may be uninvested and will therefore not generate income. The Portfolio may not achieve its investment objective during this time.

PRINCIPAL RISKS

STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share.

INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher.

GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio.

PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities.

DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities.

INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities.

MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results.

U.S. GOVERNMENT SECURITIES RISK is the risk that the U.S. government will not provide financial support to its agencies, instrumentalities or sponsored enterprises if it is not obligated to do so by law. Many U.S. government securities purchased by the Portfolio are not backed by the full faith and credit of the United States. It is possible that the issuers of such securities will not have the funds to meet their payment obligations in the future.

An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.

PORTFOLIO PERFORMANCE

The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Service Shares from year to year. There are no Premier Shares currently outstanding for the Portfolio.

The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.

Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.

CALENDAR YEAR TOTAL RETURN (SERVICE SHARES)*

* For the periods shown in the bar chart above, the highest quarterly return was 1.18% in the fourth quarter of 2006, and the lowest quarterly return was 0.00% in the fourth quarter of 2013.

AVERAGE ANNUAL TOTAL RETURNS
(For the periods ended December 31, 2013)

Average Annual Total Returns	Inception Date	1-Year	5-Year	10-Year	Since Inception
Service and Premier Shares NORTHERN INSTITUTIONAL U.S. GOVERNMENT PORTFOLIO Service Shares	Apr. 01, 1999	0.01%	0.02%	1.42%	1.96%

The 7-day yield for Service Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.

[1] Northern Trust Investments, Inc. has contractually agreed to reimburse certain expenses of the Portfolio (including the administration fee, but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses, acquired fund fees and expenses, a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries, expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio's "Other Expenses" exceed 0.10%. This contractual limitation may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Expense Reimbursement

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Service and Premier Shares | NORTHERN INSTITUTIONAL U.S. GOVERNMENT SELECT PORTFOLIO

U.S. GOVERNMENT SELECT PORTFOLIO

INVESTMENT OBJECTIVE

The Portfolio is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Portfolio seeks to maximize current income to the extent consistent with the preservation of capital and maintenance of liquidity by investing exclusively in high quality money market instruments.

FEES AND EXPENSES OF THE PORTFOLIO

This table describes the fees and expenses that you may pay if you buy and hold Service and Premier Shares of the Portfolio.

Shareholder Fees (fees paid directly from your investment)

Shareholder Fees Service and Premier Shares NORTHERN INSTITUTIONAL U.S. GOVERNMENT SELECT PORTFOLIO (USD $)	Service Shares	Premier Shares
Shareholder Fees (fees paid directly from your investment)	none	none

Annual Portfolio Operating Expenses (expenses that you pay each year as
a percentage of the value of your investment)

Annual Fund Operating Expenses Service and Premier Shares NORTHERN INSTITUTIONAL U.S. GOVERNMENT SELECT PORTFOLIO		Service Shares	Premier Shares
Management Fees		0.20%	0.20%
Other Expenses		0.38%	0.64%
Administration Fees		0.10%	0.10%
Service Agent Fees		0.25%	0.50%
Other Operating Expenses		0.03%	0.04%
Total Annual Portfolio Operating Expenses		0.58%	0.84%
Fee Waiver and Expense Reimbursement	[1]	(0.12%)	(0.12%)
Total Annual Portfolio Operating Expenses	[2]	0.46%	0.72%

EXAMPLE

The following Example is intended to help you compare the cost of investing in the Service and Premier Shares of the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Service and Premier Shares NORTHERN INSTITUTIONAL U.S. GOVERNMENT SELECT PORTFOLIO (USD $)	1 Year	3 Years	5 Years	10 Years
Service Shares	47	174	312	714
Premier Shares	74	256	454	1,026

PRINCIPAL INVESTMENT STRATEGIES

The Portfolio seeks to achieve its objective by investing, under normal circumstances, substantially all (and at least 80%) of its net assets in securities issued or guaranteed as to principal and interest by the U.S. government or by its agencies, instrumentalities or sponsored enterprises. Under normal circumstances, the Portfolio will seek to acquire only those U.S. government securities paying interest that generally is exempt from state income taxation. These securities include obligations issued by the U.S. Treasury and certain U.S. government agencies, instrumentalities or sponsored enterprises, such as the Federal Home Loan Bank and the Federal Farm Credit Banks Funding Corp.

The Securities and Exchange Commission imposes strict requirements on the investment quality, maturity, and diversification of the Portfolio’s investments. Accordingly, the Portfolio’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Portfolio’s investment adviser may consider, among other things, credit, interest rate and prepayment risks as well as general market conditions when deciding whether to buy or sell investments for the Portfolio.

Under unusual circumstances, as when appropriate securities that are exempt from state taxes are unavailable, the Portfolio also may invest in non-exempt U.S. government securities and cash equivalents, including money market funds and repurchase agreements, and hold uninvested cash. Cash assets will not generate income. The Portfolio may not achieve its investment objective during this time.

The Portfolio makes significant investments in securities issued by U.S. government-sponsored entities. Such securities are neither issued nor guaranteed by the U.S. Treasury.

PRINCIPAL RISKS

STABLE NAV RISK is the risk that the Portfolio will not be able to maintain an NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Portfolio, especially at a time when the Portfolio needs to sell securities to meet shareholder redemption requests, could cause the value of the Portfolio’s shares to decrease to a price less than $1.00 per share.

INTEREST RATE RISK is the risk that during periods of rising interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be lower than prevailing market rates; in periods of falling interest rates, the Portfolio’s yield (and the market value of its securities) will tend to be higher.

GUARANTOR (OR CREDIT ENHANCEMENT) RISK is the risk that changes in credit quality of a U.S. or foreign bank, insurance company or other financial institution or such entity’s failure to fulfill its obligations could cause the Portfolio’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Portfolio.

PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgage or other collateral of some fixed-income securities may result in a decreased rate of return and a decline in value of those securities.

DEBT EXTENSION RISK is the risk that an issuer will exercise its right to pay principal on an obligation held by the Portfolio (such as an asset-backed security) later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Portfolio will suffer from the inability to invest in higher yielding securities.

INCOME RISK is the risk that falling interest rates will cause the Portfolio’s income to decline. Income risk is generally higher for short-term debt securities.

MANAGEMENT RISK is the risk that a strategy used by the Portfolio’s investment adviser may fail to produce the intended results.

U.S. GOVERNMENT SECURITIES RISK is the risk that the U.S. government will not provide financial support to its agencies, instrumentalities or sponsored enterprises if it is not obligated to do so by law. Many U.S. government securities purchased by the Portfolio are not backed by the full faith and credit of the United States. It is possible that the issuers of such securities will not have the funds to meet their payment obligations in the future.

An investment in the Portfolio is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Portfolio.

PORTFOLIO PERFORMANCE

The bar chart and table that follow provide an indication of the risks of investing in the Portfolio by showing changes in the performance of the Portfolio’s Service Shares from year to year. There are no Premier Shares currently outstanding for the Portfolio.

The Portfolio’s past performance is not necessarily an indication of how the Portfolio will perform in the future.

Updated performance information for the Portfolio is available and may be obtained on the Portfolio’s web site at www.northerninstitutionalfunds.com or by calling 800-637-1380.

CALENDAR YEAR TOTAL RETURN (SERVICE SHARES)*

* For the periods shown in the bar chart above, the highest quarterly return was 1.20% in the fourth quarter of 2006, and the lowest quarterly return was 0.00% in the fourth quarter of 2013.

AVERAGE ANNUAL TOTAL RETURNS
(For the periods ended December 31, 2013)

Average Annual Total Returns	Inception Date	1-Year	5-Year	10-Year	Since Inception
Service and Premier Shares NORTHERN INSTITUTIONAL U.S. GOVERNMENT SELECT PORTFOLIO Service Shares	May 28, 1999	0.01%	0.02%	1.45%	1.98%

The 7-day yield for Service Shares of the Portfolio as of December 31, 2013: 0.01%. For the current 7-day yield call 800-637-1380 or visit www.northerninstitutionalfunds.com.

[1] Northern Trust Investments, Inc. has contractually agreed to limit the management fees charged to the Portfolio to 0.10% of the Portfolio's average daily net assets and to reimburse certain expenses of the Portfolio (including the administration fee, but excluding the investment advisory fee and transfer agency fee, servicing fees, extraordinary expenses such as taxes, interest, and indemnification expenses, acquired fund fees and expenses, a portion of the compensation paid to each Trustee who is not an officer, director or employee of Northern Trust Corporation or its subsidiaries, expenses related to third-party consultants engaged by the Board of Trustees of Northern Institutional Funds and membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum) to the extent the Portfolio's "Other Expenses" exceed 0.10%. These contractual limitations may not be terminated before April 1, 2015 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Portfolio. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Portfolio.

[2] After Fee Waiver and Expense Reimbursement