Prospectus: Risk/Return: Document Type Document Period End Date Registrant Name Central Index Key Amendment Flag Amendment Description Trading Symbol Document Creation Date Document Effective Date Prospectus Date Document [Axis] Prospectus Performance Measure [Axis] Before Taxes After Taxes on Distributions and Sales Return After Taxes on Distributions and Sale of Fund Shares After Taxes on Distributions Return After Taxes on Distributions Series [Axis] Series S000038425 [Member] BMO Low Volatility Equity Fund Member BMO Low Volatility Equity Fund Share Class [Axis] Share Classes C000118492 [Member] Class Y Class Y,BMO Low Volatility Equity Fund Member Class I C000118493 [Member] Class I,BMO Low Volatility Equity Fund Member Risk/Return [Heading] Objective [Heading] Objective, Primary [Text Block] Objective, Secondary [Text Block] Expense [Heading] Expense Narrative [Text Block] Shareholder Fees Caption [Text] Shareholder Fees [Table] Operating Expenses Caption [Text] Annual Fund Operating Expenses [Table] Expense Footnotes [Text Block] Expenses Deferred Charges [Text Block] Expenses Range of Exchange Fees [Text Block] Expense Example [Heading] Expense Example by Year [Heading] Expense Example Narrative [Text Block] Expense Example by, Year, Caption [Text] Expense Example, With Redemption [Table] Expense Example, No Redemption Narrative [Text Block] Expense Example, No Redemption, By Year, Caption [Text] Expense Example, No Redemption [Table] Expense Example Footnotes [Text Block] Expense Example Closing [Text Block] Portfolio Turnover [Heading] Portfolio Turnover [Text Block] Strategy [Heading] Strategy Narrative [Text Block] Risk [Heading] Risk Narrative [Text Block] Risk Footnotes [Text Block] Risk Closing [Text Block] Bar Chart and Performance Table [Heading] Performance Narrative [Text Block] Bar Chart Narrative [Text Block] Bar Chart [Heading] Bar Chart [Table] Bar Chart Footnotes [Text Block] Bar Chart Closing [Text Block] Performance Table Heading Performance Table Narrative Performance [Table] Market Index Performance [Table] Performance Table Footnotes Performance Table Closing [Text Block] Shareholder Fees: Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) Redemption Fee (as a percentage of amount redeemed, for shares held less than 30 days) Redemption Fee (as a percentage of Amount Redeemed) Redemption Fee (as a percentage of amount redeemed, for shares held less than 30 days) Shareholder Fees Column [Text] Maximum Cumulative Sales Charge (as a percentage of Offering Price) Maximum Cumulative Sales Charge (as a percentage) Maximum Deferred Sales Charge (as a percentage of Offering Price) Maximum Deferred Sales Charge (as a percentage) Maximum Sales Charge on Reinvested Dividends and Distributions (as a percentage) Redemption Fee Redemption Fee Exchange Fee (as a percentage of Amount Redeemed) Exchange Fee Maximum Account Fee (as a percentage of Assets) Maximum Account Fee Shareholder Fee, Other Operating Expenses: Management Fees Management Fees (as a percentage of Assets) Distribution (12b-1) Fees Distribution and Service (12b-1) Fees Other Expenses Other Expenses (as a percentage of Assets): Total Annual Fund Operating Expenses Expenses (as a percentage of Assets) Total Annual Fund Operating Expenses Fee Waiver and Expense Reimbursement Fee Waiver or Reimbursement Total Annual Fund Operating Expenses After Fee Waiver and Expense Reimbursement Net Expenses (as a percentage of Assets) Total Annual Fund Operating Expenses After Fee Waiver and Expense Reimbursement Operating Expenses Column [Text] Distribution or Similar (Non 12b-1) Fees Component1 Other Expenses Component2 Other Expenses Component3 Other Expenses Acquired Fund Fees and Expenses Acquired Fund Fees and Expenses Expense Example: 1 Year Expense Example, with Redemption, 1 Year 3 Years Expense Example, with Redemption, 3 Years 3 Years Expense Example, By Year, Column [Text] Column 5 Years Expense Example, with Redemption, 5 Years 5 Years 10 Years 10 Years Expense Example, with Redemption, 10 Years Expense Example, No Redemption: Expense Example, No Redemption, By Year, Column [Text] Column Expense Example, No Redemption, 1 Year 1 Year Expense Example, No Redemption, 3 Years 3 Years Expense Example, No Redemption, 5 Years 5 Years 10 Years Expense Example, No Redemption, 10 Years Bar Chart Table: Annual Return Caption [Text] Caption Annual Return, Column [Text] Column Inception Date Annual Return, Inception Date Annual Return 1990 Annual Return 1991 Annual Return 1992 Annual Return 1993 Annual Return 1994 Annual Return 1995 Annual Return 1996 Annual Return 1997 Annual Return 1998 Annual Return 1999 Annual Return 2000 Annual Return 2001 2002 Annual Return 2002 2003 Annual Return 2003 2004 Annual Return 2004 Annual Return 2005 2005 Annual Return 2006 2006 2007 Annual Return 2007 Annual Return 2008 2008 Annual Return 2009 2009 Annual Return 2010 2010 2011 Annual Return 2011 Annual Return 2012 Annual Return 2013 Annual Return 2014 Annual Return 2015 Annual Return 2016 Annual Return 2017 Annual Return 2018 Annual Return 2019 Annual Return 2020 Average Annual Return: Label 1 Year 1 Year 5 Year 5 Years 10 Years 10 Year Since Inception Since Inception Inception Date Inception Date Risk/Return Detail [Table] Fee Waiver or Reimbursement over Assets, Date of Termination Portfolio Turnover, Rate Expense Breakpoint Discounts [Text] Expense Breakpoint, Minimum Investment Required [Amount] Expense Exchange Traded Fund Commissions [Text] Expenses Represent Both Master and Feeder [Text] Expenses Explanation of Nonrecurring Account Fee [Text] Other Expenses, New Fund, Based on Estimates [Text] Acquired Fund Fees and Expenses, Based on Estimates [Text] Expenses Other Expenses Had Extraordinary Expenses Been Included [Text] Expenses Restated to Reflect Current [Text] Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text] Strategy Portfolio Concentration [Text] Risk Lose Money [Text] Risk Nondiversified Status [Text] Risk Money Market Fund [Text] Risk Not Insured Depository Institution [Text] Risk Caption Risk Column [Text] Risk [Text] Performance Information Illustrates Variability of Returns [Text] Performance One Year or Less [Text] Performance Additional Market Index [Text] Performance Availability Phone [Text] Performance Availability Website Address [Text] Performance Past Does Not Indicate Future [Text] Bar Chart Does Not Reflect Sales Loads [Text] Bar Chart, Reason Selected Class Different from Immediately Preceding Period [Text] Bar Chart, Returns for Class Not Offered in Prospectus [Text] Year to Date Return, Label Bar Chart, Year to Date Return, Date Bar Chart, Year to Date Return Highest Quarterly Return, Label Label Highest Quarterly Return, Date Highest Quarterly Return Lowest Quarterly Return, Label Label Lowest Quarterly Return, Date Lowest Quarterly Return Performance Table Does Reflect Sales Loads Performance Table Market Index Changed Index No Deduction for Fees, Expenses, Taxes [Text] Performance Table Uses Highest Federal Rate Performance Table Not Relevant to Tax Deferred Performance Table One Class of after Tax Shown [Text] Performance Table Explanation after Tax Higher Performance Table Footnotes, Reason Performance Information for Class Different from Immediately Preceding Period [Text] Caption Column Money Market Seven Day Yield, Caption [Text] Money Market Seven Day Yield Column [Text] Money Market Seven Day Yield Phone Money Market Seven Day Yield Money Market Seven Day Tax Equivalent Yield Thirty Day Yield Caption Thirty Day Yield Column [Text] Thirty Day Yield Phone Thirty Day Yield Thirty Day Tax Equivalent Yield S000000739 [Member] BMO Large-Cap Value Fund Member BMO Large-Cap Value Fund C000002136 [Member] Class Y,BMO Large-Cap Value Fund Member Class Y C000058946 [Member] Class I Class I,BMO Large-Cap Value Fund Member Russell Thousand Value. Russell Thousand Value [Member] Russell 1000® Value (reflects no deduction for fees, expenses or taxes) LLCVFI (reflects deduction of fees and no deduction for sales charges or taxes) Llcvfi [Member] LLCVFI. S000035433 [Member] BMO Dividend Income Fund Member BMO Dividend Income Fund C000108824 [Member] Class Y Class Y,BMO Dividend Income Fund Member C000108825 [Member] Class I,BMO Dividend Income Fund Member Class I BMO Large-Cap Growth Fund S000000740 [Member] BMO Large-Cap Growth Fund Member Class Y,BMO Large-Cap Growth Fund Member Class Y C000002138 [Member] C000058947 [Member] Class I Class I,BMO Large-Cap Growth Fund Member Russell Thousand Growth [Member] Russell 1000? Growth. Russell 1000® Growth (reflects no deduction for fees, expenses or taxes) Lmcgfi [Member] LMCGFI. LMCGFI (reflects deduction of fees and no deduction for sales charges or taxes) S000000741 [Member] BMO Mid-Cap Value Fund BMO Mid-Cap Value Fund Member C000002139 [Member] Class A,BMO Mid-Cap Value Fund Member Class A,BMO Mid-Cap Value Fund Member Class Y,BMO Mid-Cap Value Fund Member Class Y C000002140 [Member] Class I C000058948 [Member] Class I,BMO Mid-Cap Value Fund Member RMCVI (reflects no deduction for fees, expenses or taxes) R M C V I. R M C V I [Member] L M C V F I. 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BMO Small-Cap Value Fund S000031491 [Member] BMO Small-Cap Value Fund Member C000097896 [Member] Class Y Class Y,BMO Small-Cap Value Fund Member C000097897 [Member] Class I,BMO Small-Cap Value Fund Member Class I BMO Small-Cap Growth Fund S000000743 [Member] BMO Small-Cap Growth Fund Member Class A,BMO Small-Cap Growth Fund Member C000002143 [Member] Class A,BMO Small-Cap Growth Fund Member C000002144 [Member] Class Y,BMO Small-Cap Growth Fund Member Class Y Class I,BMO Small-Cap Growth Fund Member Class I C000058950 [Member] Russell Tow Thousand Growth [Member] Russell 2000® Growth (reflects no deduction for fees, expenses or taxes) Russell 2000? Growth. LSCGFI (reflects deduction of fees and no deduction for sales charges or taxes) Lscgfi [Member] LSCGFI. 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LEMFI (reflects deduction of fees and no deduction for sales charges or taxes) BMO Pyrford Global Strategic Return Fund Member BMO Pyrford Global Strategic Return Fund S000035435 [Member] Class Y C000108828 [Member] Class Y,BMO Pyrford Global Strategic Return Fund Member Class I C000108829 [Member] Class I,BMO Pyrford Global Strategic Return Fund Member S000026661 [Member] BMO Ultra Short Tax-Free Fund Member BMO Ultra Short Tax-Free Fund Class Y C000080027 [Member] Class Y,BMO Ultra Short Tax-Free Fund Member C000080028 [Member] Class I,BMO Ultra Short Tax-Free Fund Member Class I Blended Benchmark (reflects no deduction for fees, expenses or taxes) Blended Benchmark. Blended Benchmark [Member] B1MBI (reflects deduction of fees and no deduction for sales charges or taxes) B One Mbi [Member] B1MBI. BMO Short Tax-Free Fund Member BMO Short Tax-Free Fund S000038426 [Member] Class I,BMO Short Tax-Free Fund Member Class I C000118495 [Member] C000118494 [Member] Class Y Class Y,BMO Short Tax-Free Fund Member BMO Short-Term Income Fund Member S000000748 [Member] BMO Short-Term Income Fund C000002153 [Member] Class A,BMO Short-Term Income Fund Member Class A,BMO Short-Term Income Fund Member Class I,BMO Short-Term Income Fund Member Class I C000049011 [Member] C000002154 [Member] Class Y Class Y,BMO Short-Term Income Fund Member Ml One To Three Reflects [Member] Ml One To Three Reflects. ML 1-3 (reflects no deduction for fees, expenses or taxes) LSIGDI (reflects deduction of fees and no deduction for sales charges or taxes) Lsigdi Reflects Deduction [Member] Lsigdi Reflects Deduction. BMO Short-Intermediate Bond Fund Member BMO Short-Intermediate Bond Fund S000000746 [Member] C000002150 [Member] Class A,BMO Short-Intermediate Bond Fund Member Class A,BMO Short-Intermediate Bond Fund Member Class Y,BMO Short-Intermediate Bond Fund Member Class Y C000002151 [Member] Class I,BMO Short-Intermediate Bond Fund Member C000049010 [Member] Class I BIGCI (reflects no deduction for fees, expenses or taxes) BIGCI (reflects no deduction for fees, expenses or taxes) Bigci [Member] LSIDF (reflects deduction of fees and no deduction for sales charges or taxes) Lsidf [Member] LSIDF (reflects deduction of fees and no deduction for sales charges or taxes) BMO Intermediate Tax-Free Fund Member BMO Intermediate Tax-Free Fund S000000747 [Member] Class I C000096218 [Member] Class I,BMO Intermediate Tax-Free Fund Member Class Y Class Y,BMO Intermediate Tax-Free Fund Member C000002152 [Member] BMB 1-15 BMB 1-15 (reflects no deduction for fees, expenses or taxes) Bmb One Fifteen [Member] LIMDI (reflects deduction of fees and no deduction for sales charges or taxes) Limdi [Member] LIMDI S000000745 [Member] BMO Government Income Fund Member BMO Government Income Fund C000002148 [Member] Class A,BMO Government Income Fund Member Class A,BMO Government Income Fund Member C000002149 [Member] Class Y Class Y,BMO Government Income Fund Member C000049009 [Member] Class I Class I,BMO Government Income Fund Member BMI (reflects no deduction for fees, expenses or taxes). BMI (reflects no deduction for fees, expenses or taxes) B M I [Member] LUSMI (reflects deduction of fees and no deduction for sales charges or taxes). L U S M I [Member] LUSMI (reflects deduction of fees and no deduction for sales charges or taxes) BMO TCH Corporate Income Fund Member BMO TCH Corporate Income Fund S000024209 [Member] C000071039 [Member] Class A,BMO TCH Corporate Income Fund Member Class A,BMO TCH Corporate Income Fund Member Class I,BMO TCH Corporate Income Fund Member C000071041 [Member] Class I C000071040 [Member] Class Y Class Y,BMO TCH Corporate Income Fund Member BCCI (reflects no deduction for fees, expenses or taxes) Bcci [Member] BCCI (reflects no deduction for fees, expenses or taxes). LIIGDFI. Liigdfi [Member] LIIGDFI (reflects deduction of fees and no deduction for sales charges or taxes) BMO Aggregate Bond Fund BMO Aggregate Bond Fund Member S000017748 [Member] C000049006 [Member] Class A,BMO Aggregate Bond Fund Member Class A,BMO Aggregate Bond Fund Member C000049008 [Member] Class I,BMO Aggregate Bond Fund Member Class I Class Y,BMO Aggregate Bond Fund Member C000049007 [Member] Class Y BABI (reflects no deduction for fees, expenses or taxes). BABI (reflects no deduction for fees, expenses or taxes) Babi [Member] BMO TCH Core Plus Bond Fund Member BMO TCH Core Plus Bond Fund S000024208 [Member] C000071037 [Member] Class Y,BMO TCH Core Plus Bond Fund Member Class Y Class I C000071038 [Member] Class I,BMO TCH Core Plus Bond Fund Member Ligi [Member] LIIGI (reflects deduction of fees and no deduction for sales charges or taxes). LIIGI (reflects deduction of fees and no deduction for sales charges or taxes) BMO Monegy High Yield Bond Fund Member BMO Monegy High Yield Bond Fund S000035434 [Member] Class Y Class Y,BMO Monegy High Yield Bond Fund Member C000108826 [Member] Class I Class I,BMO Monegy High Yield Bond Fund Member C000108827 [Member] BMO TCH Emerging Markets Bond Fund S000038427 [Member] BMO TCH Emerging Markets Bond Fund Member C000118496 [Member] Class Y Class Y,BMO TCH Emerging Markets Bond Fund Member Class I,BMO TCH Emerging Markets Bond Fund Member Class I C000118497 [Member] BMO Government Money Market Fund Member S000000751 [Member] BMO Government Money Market Fund C000002160 [Member] Class I,BMO Government Money Market Fund Member Class I Class Y,BMO Government Money Market Fund Member C000002161 [Member] Class Y INGMMI (reflects deduction of fees and no deduction for sales charges or taxes) Ingmmi [Member] INGMMI (reflects deduction of fees and no deduction for sales charges or taxes). LUSGMMFI (reflects deduction of fees and no deduction for sales charges or taxes). Lusgmmfi [Member] LUSGMMFI (reflects deduction of fees and no deduction for sales charges or taxes) BMO Tax-Free Money Market Fund Member S000000750 [Member] BMO Tax-Free Money Market Fund Class Y C000002158 [Member] Class Y,BMO Tax-Free Money Market Fund Member Class I Class I,BMO Tax-Free Money Market Fund Member C000002159 [Member] Imntfnr [Member] IMNTFNR (reflects deduction of fees and no deduction for sales charges or taxes) IMNTFNR (reflects deduction of fees and no deduction for sales charges or taxes) Ltemmfi [Member] LTEMMFI (reflects deduction of fees and no deduction for sales charges or taxes) LTEMMFI (reflects deduction of fees and no deduction for sales charges or taxes) BMO Prime Money Market Fund BMO Prime Money Market Fund Member S000000749 [Member] Class A,BMO Prime Money Market Fund Member Class A,BMO Prime Money Market Fund Member C000002155 [Member] Class I Class I,BMO Prime Money Market Fund Member C000002156 [Member] C000002157 [Member] Class Y,BMO Prime Money Market Fund Member Class Y Mfra [Member] MFRA (reflects deduction of fees and no deduction for sales charges or taxes) MFRA (reflects deduction of fees and no deduction for sales charges or taxes). LMMFI (reflects deduction of fees and no deduction for sales charges or taxes) Lmmfi [Member] LMMFI (reflects deduction of fees and no deduction for sales charges or taxes).