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Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName NORTHERN FUNDS
Prospectus Date rr_ProspectusDate Jul. 31, 2013
NORTHERN MUNICIPAL MONEY MARKET FUND
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading MUNICIPAL MONEY MARKET FUND
Objective [Heading] rr_ObjectiveHeading INVESTMENT OBJECTIVE
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The Fund is a money market fund that seeks to maintain a stable net asset value (“NAV”) of $1.00 per share. The Fund 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 FUND
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 Fund.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund 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 July 31, 2014
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 Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund 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 Fund’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 Fund 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 Fund 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 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 Fund’s net assets will be invested in debt instruments that pay interest that is exempt from regular federal income tax. The Fund limits its investments in Alternative Minimum Tax (“AMT”) obligations (also known as “private activity bonds”), so that the Fund ordinarily will not invest in such obligations except during temporary defensive periods or when non-AMT obligations are unavailable. AMT obligations pay interest that may be treated as an item of tax preference to shareholders under the federal AMT. To the extent that the Fund invests in AMT obligations, a portion of the Fund’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 Fund’s investments. Accordingly, the Fund’s investments must have a remaining maturity of no more than 397 days and must be high quality. The Fund’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 Fund.

During extraordinary market conditions and interest rate environments, all or any portion of the Fund’s assets may be uninvested or invested in taxable instruments. Uninvested assets do not generate income. The Fund 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 Fund 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 Fund, especially at a time when the Fund needs to sell securities to meet shareholder redemption requests, could cause the value of the Fund’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 Fund’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 Fund’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 Fund’s investments to decline in value. Adverse developments in the banking or bond insurance industries also may negatively affect the Fund.

PREPAYMENT (OR CALL) RISK is the risk that prepayment of the underlying mortgages 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 Fund (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 Fund will suffer from the inability to invest in higher yielding securities.

INCOME RISK is the risk that falling interest rates will cause the Fund’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 Fund’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 Fund’s investments and its yield. Changes in the credit rating of a debt security held by the Fund could have a similar effect.

PROJECT/INDUSTRIAL DEVELOPMENT BOND RISK is the risk that the Fund 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 Fund to pay tax-exempt dividends.

MUNICIPAL MARKET VOLATILITY RISK is the risk that the Fund 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 Fund 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 Fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Fund.
Risk Lose Money [Text] rr_RiskLoseMoney Although the Fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Fund.
Risk Money Market Fund [Text] rr_RiskMoneyMarketFund Although the Fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the Fund 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 FUND PERFORMANCE
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The bar chart and table that follow provide an indication of the risks of investing in the Fund by showing changes in the performance of the Fund from year to year.

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

Updated performance information for the Fund is available and may be obtained on the Fund’s Web site at www.northernfunds.com or by calling 800-595-9111.
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 Fund by showing changes in the performance of the Fund from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 800-595-9111
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.northernfunds.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The Fund’s past performance is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading CALENDAR YEAR TOTAL RETURN*
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock * Year to date total return for the six months ended June 30, 2013 is 0.01%. For the periods shown in the bar chart above, the highest quarterly return was 0.81% in the third quarter of 2007, and the lowest quarterly return was 0.00% in the third quarter of 2012.
Performance Table Heading rr_PerformanceTableHeading AVERAGE ANNUAL TOTAL RETURN
(For the periods ended December 31, 2012)
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock The 7-day yield for the Fund as of December 31, 2012: 0.01%. For the current 7-day yield call 800-595-9111 or visit www.northernfunds.com.
Money Market Seven Day Yield, Caption [Text] rr_MoneyMarketSevenDayYieldCaption The 7-day yield for the Fund as of December 31, 2012
Money Market Seven Day Yield Phone rr_MoneyMarketSevenDayYieldPhone 800-595-9111
Money Market Seven Day Yield rr_MoneyMarketSevenDayYield 0.01%
NORTHERN MUNICIPAL MONEY MARKET FUND | NORTHERN MUNICIPAL MONEY MARKET FUND
  
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 0.23%
Administration Fees rr_Component1OtherExpensesOverAssets 0.10%
Transfer Agency Fees rr_Component2OtherExpensesOverAssets 0.10%
Other Operating Expenses rr_Component3OtherExpensesOverAssets 0.03%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.48%
Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.13%) [1]
Total Annual Fund Operating Expenses After Expense Reimbursement rr_NetExpensesOverAssets 0.35%
1 Year rr_ExpenseExampleYear01 36
3 Years rr_ExpenseExampleYear03 141
5 Years rr_ExpenseExampleYear05 256
10 Years rr_ExpenseExampleYear10 $ 591
2003 rr_AnnualReturn2003 0.63%
2004 rr_AnnualReturn2004 0.74%
2005 rr_AnnualReturn2005 1.95%
2006 rr_AnnualReturn2006 2.96%
2007 rr_AnnualReturn2007 3.15%
2008 rr_AnnualReturn2008 1.73%
2009 rr_AnnualReturn2009 0.16%
2010 rr_AnnualReturn2010 0.02%
2011 rr_AnnualReturn2011 0.02%
2012 rr_AnnualReturn2012 0.01%
Year to Date Return, Label rr_YearToDateReturnLabel Year to date total return
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Jun. 30, 2013
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 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 0.81%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel lowest quarterly return
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2012
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn 0.00%
1-Year rr_AverageAnnualReturnYear01 0.01%
5-Year rr_AverageAnnualReturnYear05 0.39%
10-Year rr_AverageAnnualReturnYear10 1.13%
Since Inception rr_AverageAnnualReturnSinceInception 1.95%
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 11, 1994
[1] Northern Trust Investments, Inc. has contractually agreed to reimburse a portion of the operating expenses of the Fund (other than 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 the Trust; membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum; and extraordinary expenses and interest, if any) to the extent the "Total Annual Fund Operating Expenses" exceed 0.35%. This contractual limitation may not be terminated before July 31, 2014 without the approval of the Board of Trustees. Northern Trust Investments, Inc. serves as the investment adviser and administrator to the Fund. The Northern Trust Company, an affiliate of Northern Trust Investments, Inc., serves as transfer agent, custodian and sub-administrator to the Fund.