Variable Interest Entities (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015		Dec. 31, 2014
Variable Interest Entity [Line Items]
Carrying Amount	$ 280.4	[1]	$ 360.2	[1]
Maximum exposure to loss	1,631.0		1,795.2
SBI USA Fund [Member]
Variable Interest Entity [Line Items]
Commitment funded	60.4		60.1
Carrying amount of equity investment	22.7		43.1
Maximum amount committed to invest as per agreement	75.0		75.0
JEP IV [Member]
Variable Interest Entity [Line Items]
Carrying amount of equity investment	1.0		1.2
Energy Partners I, LP [Member]
Variable Interest Entity [Line Items]
Carrying Amount	0
Maximum exposure to loss	10.0
Agency Mortgage-Backed Securitizations [Member]
Variable Interest Entity [Line Items]
Carrying Amount	2,729.5		3,186.9
Nonagency Mortgage- And Asset-Backed Securitizations [Member]
Variable Interest Entity [Line Items]
Carrying Amount	$ 930.1		$ 1,120.0

[1] There were no significant liabilities at March 31, 2015 and December 31, 2014.