Label |
Element |
Value |
Risk Return Abstract |
rr_RiskReturnAbstract |
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Registrant Name |
dei_EntityRegistrantName |
NORTHWESTERN MUTUAL SERIES FUND, INC.
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Prospectus Date |
rr_ProspectusDate |
May 01, 2025
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Large Cap Blend Portfolio |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk/Return [Heading] |
rr_RiskReturnHeading |
Large Cap Blend Portfolio – Summary
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Objective [Heading] |
rr_ObjectiveHeading |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">INVESTMENT OBJECTIVE</span>
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Objective, Primary [Text Block] |
rr_ObjectivePrimaryTextBlock |
The investment objective of the Portfolio is to seek long-term growth of capital and income.
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Expense [Heading] |
rr_ExpenseHeading |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">FEES AND EXPENSES OF THE PORTFOLIO</span>
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Expense Narrative [Text Block] |
rr_ExpenseNarrativeTextBlock |
The table below describes the fees and expenses that you may pay when you buy, hold, and sell interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher.
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Shareholder Fees Caption [Text] |
rr_ShareholderFeesCaption |
<span style="color:#000000;font-family:Times New Roman;font-size:10.02pt;font-style:italic;font-weight:bold;margin-left:0.0pt;">Shareholder Fees</span><span style="color:#000000;font-family:Times New Roman;font-size:10.02pt;margin-left:0.0pt;">(fees paid directly from your investment)</span>
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Operating Expenses Caption [Text] |
rr_OperatingExpensesCaption |
<span style="color:#000000;font-family:Times New Roman;font-size:10.02pt;font-style:italic;font-weight:bold;margin-left:0.0pt;">Annual Portfolio Operating Expenses</span><span style="color:#000000;font-family:Times New Roman;font-size:10.02pt;margin-left:0.0pt;">(expenses that you pay each year as a percentage </span><span style="color:#000000;font-family:Times New Roman;font-size:10.02pt;margin-left:0.0pt;">of the value of your investment)</span>
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Fee Waiver or Reimbursement over Assets, Date of Termination |
rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination |
<span style="color:#000000;font-family:Times New Roman;font-size:10.02pt;">April 30, 2026</span>
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Portfolio Turnover [Heading] |
rr_PortfolioTurnoverHeading |
<span style="color:#000000;font-family:Times New Roman;font-size:10pt;font-style:italic;font-weight:bold;">Portfolio Turnover</span>
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Portfolio Turnover [Text Block] |
rr_PortfolioTurnoverTextBlock |
The Portfolio pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover may indicate higher transaction costs. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 49.82% of the average value of its portfolio.
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Portfolio Turnover, Rate |
rr_PortfolioTurnoverRate |
49.82%
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Expenses Restated to Reflect Current [Text] |
rr_ExpensesRestatedToReflectCurrent |
<span style="color:#000000;font-family:Times New Roman;font-size:10.02pt;">Restated to reflect current expenses.</span>
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Expense Example [Heading] |
rr_ExpenseExampleHeading |
<span style="color:#000000;font-family:Times New Roman;font-size:10pt;font-style:italic;font-weight:bold;">Example</span>
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Expense Example Narrative [Text Block] |
rr_ExpenseExampleNarrativeTextBlock |
This Example is intended to help you compare the cost of investing in 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 or hold 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. The Example reflects adjustments made to the Portfolio’s operating expenses due to the fee waiver agreement with the investment adviser for the first year only. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
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Strategy [Heading] |
rr_StrategyHeading |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">PRINCIPAL INVESTMENT STRATEGIES</span>
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Strategy Narrative [Text Block] |
rr_StrategyNarrativeTextBlock |
Normally, the Portfolio invests at least 80% of net assets (plus any borrowings for investment purposes) in securities of large-capitalization companies. The Portfolio defines large-capitalization companies as those with a market capitalization in excess of $5 billion. The Portfolio invests primarily in securities of U.S. companies. The Portfolio may also invest up to 20% of its net assets in common stocks of foreign issuers, and may hold American Depositary Receipts (ADRs). The Portfolio may also invest in real estate investment trusts (REITs) and mid capitalization companies.In managing the Portfolio, the adviser employs a three-step process that combines a “blend” of growth-focused research, valuation and stock selection. The adviser takes an in-depth look at company prospects, which is designed to provide insight into a company’s real growth potential (e.g., sales, revenue, or earnings growth that may outpace peer averages or the overall market). The research findings allow the adviser to rank the companies in each sector according to their relative value (i.e., ranking companies from most- to least-undervalued by the market in the adviser’s assessment). Following the growth- and value-based assessments, the adviser seeks to outperform the benchmark through superior stock selection. As part of its investment process, the adviser seeks to assess the impact of environmental, social and governance (ESG) factors on many issuers in the universe in which the Portfolio invests. The adviser’s assessment is based on an analysis of key opportunities and risks across industries to seek to identify financially material issues with respect to the Portfolio’s investments in securities and ascertain key issues that merit engagement with issuers. These ESG factor assessments may not be conclusive and securities of issuers may be purchased and retained by the Portfolio for reasons other than material ESG factors while the Portfolio may divest or not invest in securities of issuers that may be positively impacted by such factors. Examples of ESG factors which may be considered (which are provided for illustrative purposes only, are not exhaustive and may not be relevant to a particular investment) are climate change risk, human capital management and executive compensation. The adviser’s ESG integration approach does not change the Portfolio’s investment objective, exclude specific types of industries or companies or limit the Portfolio’s investable universe. The Portfolio is not designed for investors who wish to screen out particular types of companies or investments or are looking for funds that meet specific ESG goals. Further, the Portfolio may hold and maintain large positions in a single or small number of securities as a result of the adviser’s investment strategy. On behalf of the Portfolio, the adviser then buys and sells equity securities, using the research and valuation rankings as a basis. In general, the adviser buys equity securities that are identified as attractively valued and considers selling them when they appear to be overvalued. Along with attractive valuation, the adviser often considers a number of other criteria:•catalysts that could trigger a rise in a stock’s price•high potential reward compared to potential risk•temporary mispricing caused by apparent market overreactions
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Risk [Heading] |
rr_RiskHeading |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">PRINCIPAL RISKS</span>
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Bar Chart and Performance Table [Heading] |
rr_BarChartAndPerformanceTableHeading |
<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">PERFORMANCE</span>
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Performance Narrative [Text Block] |
rr_PerformanceNarrativeTextBlock |
The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table to the right of the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio's returns with those of an index that represents the overall securities market (Broad-Based Index). Prior to July 31, 2023, the Portfolio was managed by a different sub-adviser. Performance shown may have been different if the current strategy, and the current sub-adviser, had been in place during the periods shown. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected.
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Performance Information Illustrates Variability of Returns [Text] |
rr_PerformanceInformationIllustratesVariabilityOfReturns |
<span style="color:#000000;font-family:Times New Roman;font-size:10.02pt;margin-left:0%;">The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table to the right of the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio's returns with those of an index that represents the overall securities market (Broad-Based Index). </span>
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Performance Past Does Not Indicate Future [Text] |
rr_PerformancePastDoesNotIndicateFuture |
<span style="color:#000000;font-family:Times New Roman;font-size:10.02pt;">Returns are based on past results and are not an </span><span style="color:#000000;font-family:Times New Roman;font-size:10.02pt;margin-left:0%;">indication of future performance.</span>
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Bar Chart Does Not Reflect Sales Loads [Text] |
rr_BarChartDoesNotReflectSalesLoads |
<span style="color:#000000;font-family:Times New Roman;font-size:10.02pt;"> Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable </span><span style="color:#000000;font-family:Times New Roman;font-size:10.02pt;margin-left:0%;">annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those </span><span style="color:#000000;font-family:Times New Roman;font-size:10.02pt;">fees and expenses were reflected.</span>
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Bar Chart Closing [Text Block] |
rr_BarChartClosingTextBlock |
Quarter/YearReturnBest Quarter4th quarter, 202015.58%Worst Quarter1st quarter, 2020-23.32%
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Performance Table Heading |
rr_PerformanceTableHeading |
<span style="color:#000000;font-family:Times New Roman;font-size:10.02pt;font-weight:bold;">Average Annual Total Return </span> <br/><span style="color:#000000;font-family:Times New Roman;font-size:10.02pt;font-weight:bold;">(for periods ended December 31, 2024)</span>
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Large Cap Blend Portfolio | Risk Lose Money [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective.
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Large Cap Blend Portfolio | Active Management Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
•Active Management Risk – The adviser’s investment strategies and techniques may not perform as expected which could cause the Portfolio to underperform other mutual funds or lose money.
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Large Cap Blend Portfolio | ADR Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
•ADR Risk – ADRs are receipts representing ownership of shares of a foreign issuer held by a U.S. bank or similar financial institution that entitle the holder to dividends and capital gains on the underlying foreign shares. ADRs are alternatives to directly purchasing the underlying foreign securities in their national markets and currencies. They are subject to many of the risks associated with direct investments in foreign securities, such as currency risk, political and economic risk and market risk, because their values depend on the performance of the non-dollar denominated underlying foreign securities. The Portfolio is also subject to fees and the credit risk of the financial institution holding the ADRs. ADRs may be “sponsored,” meaning that they are implemented by a financial institution in collaboration with the issuing foreign company, or “unsponsored,” meaning that the financial institution created the instrument without the sponsorship or direct involvement of the foreign company. Differing registration requirements apply to each type of ADR. ADRs may transact on exchanges or on over-the-counter markets (“OTC”). Conducting transactions in OTC markets may result in higher costs, a lack of pricing transparency and lower liquidity when compared with exchange-based transactions. Risks associated with different ADR types will vary, based upon differences in registration, reporting and disclosure requirements that apply to such ADRs and the characteristics of the market in which transactions for the particular ADR are conducted.
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Large Cap Blend Portfolio | Equity Securities Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
•Equity Securities Risk – The value of equity securities, such as common stocks, could decline if the financial condition of the companies the Portfolio is invested in declines or if overall market and economic conditions deteriorate. Equity securities generally have greater price volatility than fixed income securities.
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Large Cap Blend Portfolio | ESG Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
•ESG Risk – Incorporating the consideration of ESG factors in the investment process may result in the exclusion of certain securities for non-investment reasons and therefore the Portfolio may forego some market opportunities available to funds that do not consider ESG factors. The evaluation of ESG factors may affect the Portfolio’s exposure to certain issuers or industries and may not work as intended. The Portfolio may underperform other funds that do not consider ESG factors or that use different ESG factors to evaluate a security. Information used to evaluate ESG factors may not be readily available, complete, or accurate, and may vary across providers and issuers, as ESG factors are not uniformly defined or assessed. There is no guarantee that evaluating ESG considerations for individual securities will positively contribute to the Portfolio’s performance results.
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Large Cap Blend Portfolio | Foreign Investing Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
•Foreign Investing Risk – Investing in foreign securities may subject the Portfolio to more rapid and extreme changes in value or more losses than a fund that invests exclusively in U.S. securities. This risk is due to potentially smaller markets, differing reporting, accounting and auditing standards, and nationalization, expropriation or confiscatory taxation, currency blockage, political and economic conditions, or diplomatic developments. Foreign securities may be adversely affected by decreases in foreign currency values relative to the U.S. dollar and may be less liquid, more volatile, and harder to value than U.S. securities.
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Large Cap Blend Portfolio | Investment Style Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
•Investment Style Risk – A portfolio managed using a particular style of investing, such as growth or value or a combination of both, may underperform when the market does not favor the particular style used by the Portfolio. Different investment styles tend to shift in and out of favor, depending on market conditions and investor sentiment.
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Large Cap Blend Portfolio | Large Cap Company Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
•Large Cap Company Risk – Investing in large cap stocks could cause the Portfolio to underperform in markets favoring faster growing companies. Large cap stocks tend to be more mature with fewer opportunities to grow and may not have the same growth potential as stocks with smaller capitalizations.
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Large Cap Blend Portfolio | Large Position Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
•Large Position Risk – Based upon the implementation of the adviser’s investment strategy, although the Portfolio is considered “diversified” under applicable law, the Portfolio may hold and maintain large positions in a single or small number of securities. From time to time, such holdings may, on an aggregate basis, constitute a considerable percentage of Portfolio assets. As a result, the Portfolio’s performance could be significantly affected by changes in the value of a single security or small number of securities, and holding such positions may increase the overall volatility of Portfolio performance.
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Large Cap Blend Portfolio | Market Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
•Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments.
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Large Cap Blend Portfolio | Mid Cap Company Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
•Mid Cap Company Risk – Investing in mid cap stocks may cause greater risk of loss and price fluctuation than investing in stocks of larger cap companies due to a more limited track record, narrower product markets, more limited resources and less liquid trading markets. These stocks may be more volatile and more difficult to buy and sell than stocks with larger capitalizations.
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Large Cap Blend Portfolio | REITs Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
•REITs Risk – Investments in REITs are subject to the types of risks associated with investing in the real estate industry, including, among other risks: adverse developments affecting the real estate industry; declines in real property values; changes in interest rates; defaults by mortgagors or other borrowers and tenants; lack of availability of mortgage funds or financing; extended vacancies of properties, especially during economic downturns; casualty or condemnation losses; property taxes and operating losses; and governmental actions, such as changes to tax laws, zoning regulations or environmental regulations. REITs are dependent upon the quality of their management, may have limited financial resources and heavy cash flow dependency, may not be diversified geographically or by property type, and may be subject to self-liquidation.
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Large Cap Blend Portfolio | Sector Focus Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
•Sector Focus Risk – To the extent the Portfolio invests a relatively high percentage of its assets in a particular sector, it will have greater exposure to the risks associated with that sector, including the risk that the securities of companies within the sector will underperform due to adverse economic conditions, regulatory or legislative changes, or increased competition affecting the sector. To the extent the Portfolio underweight in other sectors, the Portfolio risks missing out on advances in those sectors.
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Large Cap Blend Portfolio | Underlying Portfolio Risk [Member] |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Risk [Text Block] |
rr_RiskTextBlock |
•Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so.
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Large Cap Blend Portfolio | Large Cap Blend Portfolio |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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Shareholder Fees(fees paid directly from your investment) |
rr_ShareholderFeeOther |
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Management Fee |
rr_ManagementFeesOverAssets |
0.76%
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Distribution and Service (12b-1) Fees |
rr_DistributionAndService12b1FeesOverAssets |
none
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Other Expenses |
rr_OtherExpensesOverAssets |
0.08%
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Total Annual Portfolio Operating Expenses |
rr_ExpensesOverAssets |
0.84%
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Fee Waiver |
rr_FeeWaiverOrReimbursementOverAssets |
(0.12%)
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[1],[2] |
Total Annual Portfolio Operating Expenses After Fee Waiver |
rr_NetExpensesOverAssets |
0.72%
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[1],[2] |
1 Year |
rr_ExpenseExampleYear01 |
$ 74
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3 Years |
rr_ExpenseExampleYear03 |
256
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5 Years |
rr_ExpenseExampleYear05 |
454
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10 Years |
rr_ExpenseExampleYear10 |
$ 1,026
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2015 |
rr_AnnualReturn2015 |
(2.42%)
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2016 |
rr_AnnualReturn2016 |
13.99%
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2017 |
rr_AnnualReturn2017 |
19.02%
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2018 |
rr_AnnualReturn2018 |
(4.00%)
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2019 |
rr_AnnualReturn2019 |
23.97%
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2020 |
rr_AnnualReturn2020 |
10.05%
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2021 |
rr_AnnualReturn2021 |
18.46%
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2022 |
rr_AnnualReturn2022 |
(13.78%)
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2023 |
rr_AnnualReturn2023 |
20.61%
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2024 |
rr_AnnualReturn2024 |
23.86%
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Highest Quarterly Return, Label |
rr_HighestQuarterlyReturnLabel |
<span style="color:#000000;font-family:Times New Roman;font-size:9.02pt;margin-left:0.0pt;">Best Quarter</span>
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Highest Quarterly Return, Date |
rr_BarChartHighestQuarterlyReturnDate |
Dec. 31, 2020
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Highest Quarterly Return |
rr_BarChartHighestQuarterlyReturn |
15.58%
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Lowest Quarterly Return, Label |
rr_LowestQuarterlyReturnLabel |
<span style="color:#000000;font-family:Times New Roman;font-size:9.02pt;margin-left:0.0pt;">Worst Quarter</span>
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Lowest Quarterly Return, Date |
rr_BarChartLowestQuarterlyReturnDate |
Mar. 31, 2020
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Lowest Quarterly Return |
rr_BarChartLowestQuarterlyReturn |
(23.32%)
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1 Yr |
rr_AverageAnnualReturnYear01 |
23.86%
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5 Yr |
rr_AverageAnnualReturnYear05 |
10.92%
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10 Yr |
rr_AverageAnnualReturnYear10 |
10.22%
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Large Cap Blend Portfolio | S&P 500® Index(reflects no deduction for fees, expenses or taxes) |
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Risk Return Abstract |
rr_RiskReturnAbstract |
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1 Yr |
rr_AverageAnnualReturnYear01 |
25.02%
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5 Yr |
rr_AverageAnnualReturnYear05 |
14.53%
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10 Yr |
rr_AverageAnnualReturnYear10 |
13.10%
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