Variable Interest Entities (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Maximum exposure to loss	$ 1,417.0	$ 1,461.1
Carrying Amount	439.4	389.2
Securitization Vehicles [Member]
Variable Interest Entity [Line Items]
Aggregated Loan Receivables	228.3
Private Equity Vehicles [Member] | Energy Partners I, LP [Member]
Variable Interest Entity [Line Items]
Maximum exposure to loss	3.0	3.0
Real Estate Investment Vehicles [Member]
Variable Interest Entity [Line Items]
Equity commitments	98.0
Funded equity commitments	86.5
Maximum exposure to loss	100.5
Carrying Amount	89.0
Other Private Investment Vehicles [Member]
Variable Interest Entity [Line Items]
Equity commitments	102.9	76.4
Funded equity commitments	98.6	73.0
Carrying amount of equity investment	90.1	88.0
Maximum exposure to loss	92.9	91.4
Carrying Amount	90.1	88.0
Agency Mortgage-Backed Securitizations [Member]
Variable Interest Entity [Line Items]
Carrying Amount	1,647.7	3,359.1
Nonagency Mortgage- And Asset-Backed Securitizations [Member]
Variable Interest Entity [Line Items]
Carrying Amount	527.0	630.5
JCP Entities [Member] | Private Equity Vehicles [Member]
Variable Interest Entity [Line Items]
Equity commitments	148.1	148.1
Funded equity commitments	124.9	124.6
Carrying amount of equity investment	$ 32.0	$ 39.3