Accounting Policies (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2016	Dec. 31, 2015
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Net waivers	$ 1.1	$ 5.5
Assets	24,137.7	24,137.7	$ 25,073.2
Liabilities and equity	24,137.7	24,137.7	$ 25,073.2
Accounting Standards Update 2015-02 [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Assets	3,170.6	3,170.6
Liabilities and equity	3,170.6	3,170.6
Collateralized Loan Obligations [Member] | Accounting Standards Update 2015-02 [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Assets	2,366.5	2,366.5
Liabilities and equity	2,366.5	2,366.5
Consolidation, Eliminations [Member] | Accounting Standards Update 2015-02 [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Assets	458.5	458.5
Liabilities and equity	458.5	458.5
Waiver [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Management and administrative fees	$ 3.3	$ 12.3
Change in third party distribution service and advisory fee	67.00%	55.00%