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The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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This item represents an other than temporary decline in value that has been recognized against an investment accounted for under the equity method of accounting. The excess of the carrying amount over the fair value of the investment represents the amount of the write down which is or was reflected in earnings. The written down value is a new cost basis with the adjusted value of the investment becoming its new carrying value subject to the equity accounting method. Evidence of a loss in value might include, but would not necessarily be limited to, absence of an ability to recover the carrying amount of the investment or inability of the investee to sustain an earnings capacity which would justify the carrying amount of the investment.

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Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of income (loss) for proportionate share of equity method investee's income (loss).

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Amount of commitment classified as other to be paid in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Equity Method Investments in Affiliates - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended						12 Months Ended
	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Estimated Future Amortization Expense of Finite-Lived Intangibles
Equity method investments in Affiliates (net)	$ 2,074.8		$ 2,195.6				$ 2,074.8	$ 2,195.6
Other liabilities	452.2		359.1				452.2	359.1
Equity method loss (net)							(43.4)	(338.0)	$ (0.2)
Equity Method Investee
Estimated Future Amortization Expense of Finite-Lived Intangibles
Impairment of equity method investment	$ 45.0	$ 140.0	$ 60.0	$ 10.0		$ 415.0
Fair value assumptions, average projected growth period	5 years	5 years				5 years
Fair value assumptions, average projected growth rate			9.00%	(20.00%)		(13.00%)
Fair value assumptions, discount rate for asset based fees			11.00%	11.00%		11.00%
Fair value assumptions, discount rate for performance based fees			20.00%	20.00%		20.00%
Fair value assumptions, market participant tax rate			25.00%	25.00%		25.00%
Equity method investments in Affiliates (net)	$ 2,074.8		$ 2,195.6				2,074.8	2,195.6	2,791.0
Undistributed earnings from equity method affiliates	170.6						170.6
Contingent payments due
2021	35.0						35.0
2022	37.5						37.5
Equity Method Investee \| Achievement of Specified Financial Targets
Estimated Future Amortization Expense of Finite-Lived Intangibles
Equity method investments in Affiliates (net)	40.0						40.0
Other liabilities	$ 40.0						40.0
Equity Method Investee \| Minimum
Estimated Future Amortization Expense of Finite-Lived Intangibles
Fair value assumptions, average projected growth rate		(2.00%)
Fair value assumptions, discount rate for asset based fees	11.00%	11.00%
Fair value assumptions, discount rate for performance based fees	20.00%	20.00%
Fair value assumptions, market participant tax rate	25.00%	25.00%
Equity Method Investee \| Maximum
Estimated Future Amortization Expense of Finite-Lived Intangibles
Fair value assumptions, average projected growth rate	(5.00%)
Acquired Client Relationships Under Equity Method Investments \| Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Intangible amortization expense							147.0	$ 142.4	$ 97.5
Estimated Future Amortization Expense of Finite-Lived Intangibles
Intangible future amortization expense in 2021	$ 120.0						120.0
Intangible future amortization expense in 2022	50.0						50.0
Intangible future amortization expense in 2023	50.0						50.0
Intangible future amortization expense in 2024	50.0						50.0
Intangible future amortization expense in 2025	$ 50.0						$ 50.0
Non-US \| Equity Method Investee
Estimated Future Amortization Expense of Finite-Lived Intangibles
Noncontrolling interest, sale of ownership percentage					5.00%
Payments to noncontrolling interests					$ 25.7