Summary of Significant Accounting Polices and Adoption of New Accounting Pronouncements (Details) - USD ($) $ in Millions		114 Months Ended
		Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Negative fund performance that would cause reversal of performance fees		$ 31.1
Accrued performance fees		3.8		$ 9.1
Noncontrolling interests		1,324.2	$ 1,295.1
Cumulative effect of ASU 2016-09 adoption	[1]	9.3
Retained Earnings (Accumulated Deficit) [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Cumulative effect of ASU 2016-09 adoption	[1]	9.3
Accounting Standards Update 2016-09 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Increase in deferred tax asset			9.3
Accounting Standards Update 2016-09 [Member] | Retained Earnings (Accumulated Deficit) [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Cumulative effect of ASU 2016-09 adoption		9.3	9.3
KWE [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Noncontrolling interests		$ 1,100.0	$ 1,300.0

[1] See Note 2 for further discussion.