Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	NORTHERN FUNDS
Prospectus Date	rr_ProspectusDate	Oct. 02, 2012
U.S.TREASURY INDEX FUND
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	U.S. TREASURY INDEX FUND
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Fund seeks to provide investment results approximating the performance of the Barclays U.S. Treasury Index.
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	November 30, 2013
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	PORTFOLIO TURNOVER.
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual portfolio operating expenses or in the Example, affect the Fund’s performance. During its most recent fiscal year, the Northern Institutional U.S. Treasury Index Portfolio’s (the “Predecessor U.S. Treasury Index Fund”) turnover rate was 64.52% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	64.52%
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	Under normal circumstances, the Fund will invest substantially all (and at least 80%) of its net assets in a representative sample of the U.S. Treasury obligations included in the Barclays U.S. Treasury Index. The Fund will buy and sell securities with the goal of achieving an overall duration and total return similar to that of the Barclays U.S. Treasury Index. The Barclays U.S. Treasury Index is an unmanaged index that includes a broad range of U.S. Treasury obligations and is considered representative of U.S. Treasury bond performance overall. As of July 30, 2012, the duration of the Barclays U.S. Treasury Index was 5.72 years. The Fund is passively managed, which means it tries to duplicate the investment composition and performance of the Barclays U.S. Treasury Index using computer programs and statistical procedures. Because the Fund will have fees and transaction expenses (while the Barclays U.S. Treasury Index has none), returns are likely to be below those of the Barclays U.S. Treasury Index. The Investment Adviser expects that, under normal circumstances, the quarterly performance of the Fund, before expenses, will track the performance of the Barclays U.S. Treasury Index within a 0.95 correlation coefficient. Barclays Capital, Inc. (“Barclays Capital”) does not endorse any of the securities in the Barclays U.S. Treasury Index. It is not a sponsor of the Fund and is not affiliated with the Fund in any way.
Risk [Heading]	rr_RiskHeading	PRINCIPAL RISKS
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	MARKET RISK is the risk that the market values of fixed-income securities owned by the Fund may decline, at times sharply and unpredictably. MANAGEMENT RISK is the risk that a strategy used by the investment management team may fail to produce the intended results. LIQUIDITY RISK is the risk that certain portfolio securities may be less liquid than others, which may make them difficult or impossible to sell at the time and the price that the Fund would like, adversely affecting the value of the Fund’s investments and its returns. INTEREST RATE/MATURITY RISK is the risk that the value of the Fund’s assets will decline because of rising interest rates. This risk is generally lower for funds that have shorter-weighted maturities, such as money market funds and short-term bond funds. The magnitude of this decline will often be greater for longer-term fixed-income securities than shorter-term fixed income securities. 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 Fund (such as a mortgage-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. TRACKING RISK is the risk that the Fund’s performance may vary substantially from the performance of the benchmark index it tracks as a result of share purchases and redemptions, transaction costs, expenses and other factors. As with any mutual fund, it is possible to lose money on an investment in the Fund. 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.
Risk Lose Money [Text]	rr_RiskLoseMoney	As with any mutual fund, it is possible to lose money on an investment 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. It is currently contemplated that before the Fund commences operations, substantially all of the assets of the Predecessor U.S. Treasury Index Fund, another portfolio advised by the Investment Adviser, will be transferred to the Fund in a tax-free reorganization (the “Reorganization”), which is expected to occur on or about November 16, 2012. The Predecessor U.S. Treasury Index Fund was managed with the same investment objective, strategies and policies as will be followed by the Fund. As a result of the Reorganization, the performance and accounting history of the Predecessor U.S. Treasury Index Fund prior to the date of the Reorganization will be assumed by the Fund. The performance information set forth in the bar chart and table below is that of the Class A Shares of the Predecessor U.S. Treasury Index Fund, which commenced operations on January 11, 1993. The Predecessor U.S. Treasury Index Fund’s past performance, before and after taxes, 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.
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 Predecessor U.S. Treasury Index Fund’s past performance, before and after taxes, is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	CALENDAR YEAR TOTAL RETURN (CLASS A)*
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	* For the periods shown in the bar chart above, the highest quarterly return was 8.80% in the fourth quarter of 2008, and the lowest quarterly return was (3.24)% in the second quarter of 2004.
Performance Table Heading	rr_PerformanceTableHeading	AVERAGE ANNUAL TOTAL RETURNS (For the periods ended December 31, 2011)
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
U.S.TREASURY INDEX FUND | U.S.TREASURY INDEX FUND
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fees	rr_ManagementFeesOverAssets	0.30%
Other Expenses	rr_OtherExpensesOverAssets	0.36%
Administration Fees	rr_Component1OtherExpensesOverAssets	0.15%
Transfer Agency Fees	rr_Component2OtherExpensesOverAssets	0.10%
Other Operating Expenses	rr_Component3OtherExpensesOverAssets	0.11%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.66%
Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.51%)	[1]
Total Annual Fund Operating Expenses After Expense Reimbursement	rr_NetExpensesOverAssets	0.15%
1 Year	rr_ExpenseExampleYear01	15
3 Years	rr_ExpenseExampleYear03	160
5 Years	rr_ExpenseExampleYear05	317
10 Years	rr_ExpenseExampleYear10	774
2002	rr_AnnualReturn2002	11.57%
2003	rr_AnnualReturn2003	2.13%
2004	rr_AnnualReturn2004	3.30%
2005	rr_AnnualReturn2005	2.61%
2006	rr_AnnualReturn2006	2.80%
2007	rr_AnnualReturn2007	8.92%
2008	rr_AnnualReturn2008	13.79%
2009	rr_AnnualReturn2009	(3.58%)
2010	rr_AnnualReturn2010	5.57%
2011	rr_AnnualReturn2011	9.60%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Dec. 31, 2008
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	8.80%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Jun. 30, 2004
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(3.24%)
1-Year	rr_AverageAnnualReturnYear01	9.60%
5-Year	rr_AverageAnnualReturnYear05	6.70%
10-Year	rr_AverageAnnualReturnYear10	5.55%
Since Inception	rr_AverageAnnualReturnSinceInception	6.17%
Inception Date	rr_AverageAnnualReturnInceptionDate	Jan. 11, 1993
U.S.TREASURY INDEX FUND | Return after taxes on distributions | U.S.TREASURY INDEX FUND
Risk/Return:	rr_RiskReturnAbstract
1-Year	rr_AverageAnnualReturnYear01	8.45%
5-Year	rr_AverageAnnualReturnYear05	5.29%
10-Year	rr_AverageAnnualReturnYear10	4.06%
Since Inception	rr_AverageAnnualReturnSinceInception	4.21%
U.S.TREASURY INDEX FUND | Return after taxes on distributions and sale of Fund shares | U.S.TREASURY INDEX FUND
Risk/Return:	rr_RiskReturnAbstract
1-Year	rr_AverageAnnualReturnYear01	6.65%
5-Year	rr_AverageAnnualReturnYear05	5.00%
10-Year	rr_AverageAnnualReturnYear10	3.94%
Since Inception	rr_AverageAnnualReturnSinceInception	4.12%
U.S.TREASURY INDEX FUND | Barclays U.S. Treasury Index (reflects no deduction for fees, expenses, or taxes)
Risk/Return:	rr_RiskReturnAbstract
1-Year	rr_AverageAnnualReturnYear01	9.81%
5-Year	rr_AverageAnnualReturnYear05	6.81%
10-Year	rr_AverageAnnualReturnYear10	5.71%
Since Inception	rr_AverageAnnualReturnSinceInception	6.36%

[1] Northern Trust Investments, Inc. (the "Investment Adviser") has contractually agreed to reimburse certain expenses of the Fund (excluding 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 Fund; membership dues paid to the Investment Company Institute and Mutual Fund Directors Forum; extraordinary expenses; and interest, if any) to the extent the "Total Annual Fund Operating Expenses After Expense Reimbursement" exceed 0.15%. This contractual limitation may not be terminated before November 30, 2013 without the approval of the Fund's Board of Trustees.