Borrowings - Outstanding Loans Payable of Consolidated Funds (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Borrowing Outstanding	$ 3,725.1	$ 3,876.6
Fair Value	3,721.2	3,866.3
Senior secured notes
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Borrowing Outstanding	3,539.7	3,681.0
Fair Value	$ 3,544.7	$ 3,672.5
Weighted Average Interest Rate (as a percent)	2.22%	2.45%
Weighted Average Remaining Maturity in Years	11 years 8 months 23 days	10 years 2 months 19 days
Subordinated notes, preferred shares and other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Borrowing Outstanding	$ 185.4	$ 195.6
Fair Value	$ 176.5	$ 193.8
Weighted Average Remaining Maturity in Years	9 years 7 months 17 days	9 years 3 months 3 days