Investment Securities (Asset backed securities) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013		Mar. 31, 2013		Dec. 31, 2012
Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 1,693.7		$ 1,753.1
Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	213.5	[1]	201.9	[1]	201.8	[1]	198.9	[1]
Fixed rate CMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Average basis points of subordination	3000.00%
Fixed rate CMBS | Fair Value
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	127.9
Floating rate CMBS | Fair Value
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	41.3
GNMA | Fair Value
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	305.9		321.8
GNMA | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	305.9		321.8
GNMA | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0		0
FNMA | Fair Value
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	64.8		36.5
FNMA | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	64.8		36.5
FNMA | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0		0
FHLMC | Fair Value
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	23.0		24.3
FHLMC | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	23.0		24.3
FHLMC | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0		0
Agency commercial mortgage-backed securities | Fair Value
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	393.7	[2]	382.6	[2]
Agency commercial mortgage-backed securities | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	393.7	[2]	382.6	[2]
Agency commercial mortgage-backed securities | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0	[2]	0	[2]
Residential
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	54.0
Residential | Fair Value
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	54.0		51.5
Residential | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	54.0		51.5
Residential | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0		0
Commercial | Fair Value
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	169.2		155.0
Commercial | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	161.7		155.0
Commercial | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	7.5		0
Total Non-agency | Fair Value
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	223.2		206.5
Total Non-agency | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	215.7		206.5
Total Non-agency | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	7.5		0
Total mortgage-backed securities | Fair Value
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	616.9		589.1
Total mortgage-backed securities | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	609.4		589.1
Total mortgage-backed securities | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	7.5		0
Credit card receivables | Fair Value
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	101.8		124.2
Credit card receivables | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	90.9		113.3
Credit card receivables | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	10.9		10.9
Vehicle receivables | Fair Value
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	115.8		189.3
Vehicle receivables | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	115.8		189.3
Vehicle receivables | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0		0
Other | Fair Value
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	46.8		46.9
Other | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	46.8		46.9
Other | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0		0
Total other asset-backed securities | Fair Value
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	264.4		360.4
Total other asset-backed securities | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	253.5		349.5
Total other asset-backed securities | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	10.9		10.9
Total mortgage-backed and asset-backed securities | Fair Value
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	881.3		949.5
Total mortgage-backed and asset-backed securities | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	862.9		938.6
Total mortgage-backed and asset-backed securities | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	18.4		10.9
Non-Prime Residential Mortgage Backed Security | Fair Value
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 6.4
Maximum | Commercial
Schedule of Trading Securities and Other Trading Assets [Line Items]
Percentage of underlying loans reported as non-performing	1.00%

[1] Excludes the carrying value of $19.3 million and $20.6 million associated with a tax advantaged federal affordable housing development fund accounted for using the equity method as of March 31, 2014 and 2013, respectively.

[2] Represents publicly traded mortgage-backed securities which carry the full faith and credit guaranty of the U.S. government (i.e., GNMA) or are guaranteed by a government sponsored entity (i.e., FNMA, FHLMC).