Accrued Performance Fees - Components of Accrued Performance Fee (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Accrued performance fees	$ 3,670.6	$ 2,481.1
Corporate Private Equity
Segment Reporting Information [Line Items]
Accrued performance fees	2,272.4	1,375.4
Real Assets
Segment Reporting Information [Line Items]
Accrued performance fees	657.5	483.4
Global Credit
Segment Reporting Information [Line Items]
Accrued performance fees	56.1	68.6
Investment Solutions
Segment Reporting Information [Line Items]
Accrued performance fees	$ 684.6	$ 553.7