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v2.4.1.9

Segment Information - Schedule of Segment Information (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2014 | Sep. 30, 2014 | Jun. 30, 2014 | Mar. 31, 2014 | Dec. 31, 2013 | Sep. 30, 2013 | Jun. 30, 2013 | Mar. 31, 2013 | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Segment Reporting Information |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue | $ 641.2 us-gaap_AssetManagementFees1 | $ 640.3 us-gaap_AssetManagementFees1 | [1] | $ 636.3 us-gaap_AssetManagementFees1 | [1] | $ 593.1 us-gaap_AssetManagementFees1 | $ 594.0 us-gaap_AssetManagementFees1 | $ 551.6 us-gaap_AssetManagementFees1 | $ 541.0 us-gaap_AssetManagementFees1 | $ 502.2 us-gaap_AssetManagementFees1 | $ 2,510.9 us-gaap_AssetManagementFees1 | $ 2,188.8 us-gaap_AssetManagementFees1 | $ 1,805.5 us-gaap_AssetManagementFees1
Net income (controlling interest) | 172.6 us-gaap_NetIncomeLoss | 103.2 us-gaap_NetIncomeLoss | [1] | 99.1 us-gaap_NetIncomeLoss | [1] | 77.2 us-gaap_NetIncomeLoss | 158.2 us-gaap_NetIncomeLoss | 75.2 us-gaap_NetIncomeLoss | 64.7 us-gaap_NetIncomeLoss | 62.4 us-gaap_NetIncomeLoss | 452.1 us-gaap_NetIncomeLoss | 360.5 us-gaap_NetIncomeLoss | 174.0 us-gaap_NetIncomeLoss
Total assets | 7,698.1 us-gaap_Assets |  |  |  |  |  | 6,318.8 us-gaap_Assets |  |  |  | 7,698.1 us-gaap_Assets | 6,318.8 us-gaap_Assets | 6,187.1 us-gaap_Assets
Goodwill | 2,652.8 us-gaap_Goodwill |  |  |  |  |  | 2,341.7 us-gaap_Goodwill |  |  |  | 2,652.8 us-gaap_Goodwill | 2,341.7 us-gaap_Goodwill | 2,355.2 us-gaap_Goodwill
Equity method investments in Affiliates | 1,031.3 us-gaap_EquityMethodInvestments |  |  |  |  |  | 1,123.3 us-gaap_EquityMethodInvestments |  |  |  | 1,031.3 us-gaap_EquityMethodInvestments | 1,123.3 us-gaap_EquityMethodInvestments | 1,783.5 us-gaap_EquityMethodInvestments
Institutional |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  |  | 1,022.8 us-gaap_AssetManagementFees1 / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember | 948.7 us-gaap_AssetManagementFees1 / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember | 861.3 us-gaap_AssetManagementFees1 / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember
Net income (controlling interest) |  |  |  |  |  |  |  |  |  |  | 227.0 us-gaap_NetIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember | 219.9 us-gaap_NetIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember | 126.0 us-gaap_NetIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember
Total assets | 3,739.8 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember |  |  |  |  |  | 3,196.5 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember |  |  |  | 3,739.8 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember | 3,196.5 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember | 3,176.5 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember
Goodwill | 1,159.1 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember |  |  |  |  |  | 1,076.3 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember |  |  |  | 1,159.1 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember | 1,076.3 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember | 1,078.5 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember
Equity method investments in Affiliates | 879.6 us-gaap_EquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember |  |  |  |  |  | 942.6 us-gaap_EquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember |  |  |  | 879.6 us-gaap_EquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember | 942.6 us-gaap_EquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember | 1,533.8 us-gaap_EquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = amg_InstitutionalMember
Mutual Fund |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  |  | 1,242.6 us-gaap_AssetManagementFees1 / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember | 1,023.0 us-gaap_AssetManagementFees1 / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember | 774.4 us-gaap_AssetManagementFees1 / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember
Net income (controlling interest) |  |  |  |  |  |  |  |  |  |  | 180.1 us-gaap_NetIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember | 103.4 us-gaap_NetIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember | 27.3 us-gaap_NetIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember
Total assets | 3,082.0 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember |  |  |  |  |  | 2,448.4 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember |  |  |  | 3,082.0 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember | 2,448.4 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember | 2,354.8 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember
Goodwill | 1,125.3 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember |  |  |  |  |  | 928.1 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember |  |  |  | 1,125.3 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember | 928.1 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember | 939.5 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember
Equity method investments in Affiliates | 81.2 us-gaap_EquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember |  |  |  |  |  | 77.7 us-gaap_EquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember |  |  |  | 81.2 us-gaap_EquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember | 77.7 us-gaap_EquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember | 150.3 us-gaap_EquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = amg_MutualFundMember
High Net Worth |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  |  | 245.5 us-gaap_AssetManagementFees1 / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember | 217.1 us-gaap_AssetManagementFees1 / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember | 169.8 us-gaap_AssetManagementFees1 / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember
Net income (controlling interest) |  |  |  |  |  |  |  |  |  |  | 45.0 us-gaap_NetIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember | 37.2 us-gaap_NetIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember | 20.7 us-gaap_NetIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember
Total assets | 876.3 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember |  |  |  |  |  | 673.9 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember |  |  |  | 876.3 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember | 673.9 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember | 655.8 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember
Goodwill | 368.4 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember |  |  |  |  |  | 337.3 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember |  |  |  | 368.4 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember | 337.3 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember | 337.2 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember
Equity method investments in Affiliates | $ 70.5 us-gaap_EquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember |  |  |  |  |  | $ 103.0 us-gaap_EquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember |  |  |  | $ 70.5 us-gaap_EquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember | $ 103.0 us-gaap_EquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember | $ 99.4 us-gaap_EquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = amg_HighNetWorthMember
[1] | In the fourth quarter of 2014, the Company finalized its purchase price allocation for its investment in EIG. The final purchase price allocation resulted in a change in Income from equity method investments and Intangible-related deferred taxes in the second and third quarters of 2014. Income before taxes decreased $1.6 million and $1.7 million in the second and third quarters, respectively, Net income (controlling interest) decreased $1.0 million and $1.1 million in the second and third quarters, respectively, and Earnings per share (diluted) decreased $0.02 in both periods.

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