Goodwill and Other Intangible Assets - Indefinite-Lived Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Indefinite Lived Intangible Assets
Net carrying amount of unamortized indefinite lived intangible assets	$ 790.6	$ 833.0
WM Advisors, Inc.
Indefinite Lived Intangible Assets
Net carrying amount of unamortized indefinite lived intangible assets	608.0	$ 608.0
Operating expenses \| Brazil mutual fund company
Indefinite Lived Intangible Assets
Indefinite lived intangible asset impairment	$ 14.7

Amount of impairment loss resulting from write-down of assets, excluding financial assets and goodwill, lacking physical substance and having a projected indefinite period of benefit to fair value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16373-109275

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- Definition

Amount of assets, excluding financial assets and goodwill, lacking physical substance and having a projected indefinite period of benefit.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275

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