Accounting Policies Accounting Policies (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Change in Third party distribution service and advisory fee			50.40%
Net Waivers	$ (1.9)		$ 4.5
Assets	23,502.8	$ 23,502.8		$ 25,073.2
Liabilities and Equity	23,502.8	23,502.8		$ 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]
Investment Advisory, Management and Administrative Fees	$ 4.1	$ 9.0
Change in Third party distribution service and advisory fee	54.00%