Variable Interest Entities (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Variable Interest Entity [Line Items]
Carrying Amount	$ 286.8	$ 360.2
Maximum exposure to loss	1,545.9	1,795.2
SBI USA Fund [Member]
Variable Interest Entity [Line Items]
Maximum amount committed to invest as per agreement	75.0	75.0
Commitment funded	60.4	60.1
Carrying amount of equity investment	23.2	43.1
JEP IV [Member]
Variable Interest Entity [Line Items]
Carrying amount of equity investment	1.1	1.2
Energy Partners I, LP [Member]
Variable Interest Entity [Line Items]
Carrying Amount	0.0
Maximum exposure to loss	10.0
Agency Mortgage-Backed Securitizations [Member]
Variable Interest Entity [Line Items]
Carrying Amount	3,098.7	3,186.9
Nonagency Mortgage- And Asset-Backed Securitizations [Member]
Variable Interest Entity [Line Items]
Carrying Amount	$ 983.7	$ 1,120.0