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v2.4.1.9

Intangible Assets - Schedule of Changes in Goodwill (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended
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Mar. 31, 2015
Goodwill [Roll Forward] |
Beginning balance (in dollars) | $ 2,652.8 us-gaap_Goodwill
Goodwill acquired | 0 us-gaap_GoodwillAcquiredDuringPeriod
Foreign currency translation | (31.6)us-gaap_GoodwillTranslationAdjustments
Ending balance (in dollars) | 2,621.2 us-gaap_Goodwill
Institutional |
Goodwill [Roll Forward] |
Beginning balance (in dollars) | 1,159.1 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember
Goodwill acquired | 0 us-gaap_GoodwillAcquiredDuringPeriod / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember
Foreign currency translation | (17.9)us-gaap_GoodwillTranslationAdjustments / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember
Ending balance (in dollars) | 1,141.2 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember
Mutual Fund |
Goodwill [Roll Forward] |
Beginning balance (in dollars) | 1,125.3 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember
Goodwill acquired | 0 us-gaap_GoodwillAcquiredDuringPeriod / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember
Foreign currency translation | (3.5)us-gaap_GoodwillTranslationAdjustments / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember
Ending balance (in dollars) | 1,121.8 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember
High Net Worth |
Goodwill [Roll Forward] |
Beginning balance (in dollars) | 368.4 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember
Goodwill acquired | 0 us-gaap_GoodwillAcquiredDuringPeriod / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember
Foreign currency translation | (10.2)us-gaap_GoodwillTranslationAdjustments / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember
Ending balance (in dollars) | $ 358.2 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember

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- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266 + Details
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Balance Type: | debit
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- Definition Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 + Details
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- Details
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- Definition Amount of increase (decrease) from foreign currency translation adjustments of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 + Details
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- Details
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Data Type: | na
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Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Data Type: | na
Balance Type: |
Period Type: |