Investment Securities (Mortgage-backed Asset Securities) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012		Jun. 30, 2012		Dec. 31, 2011
Level 2 Inputs
Investment securities
Fair value investments	$ 4,721.2		$ 5,206.1		$ 5,006.4		$ 6,088.2
Level 2 Inputs | Government National Mortgage Association Certificates and Obligations (GNMA)
Investment securities
Fair value investments	818.0		1,013.4
Level 2 Inputs | Federal National Mortgage Association Certificates and Obligations (FNMA)
Investment securities
Fair value investments	52.5		74.6
Level 2 Inputs | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC)
Investment securities
Fair value investments	47.8		55.8
Level 2 Inputs | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Investment securities
Fair value investments	918.3	[1]	1,143.8	[1]
Level 2 Inputs | Residential Mortgage Backed Securities
Investment securities
Fair value investments	109.6		160.6
Level 2 Inputs | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	300.3		334.1
Level 2 Inputs | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	409.9		494.7
Level 2 Inputs | Collateralized Mortgage Backed Securities
Investment securities
Fair value investments	1,328.2		1,638.5
Level 2 Inputs | Collateralized Credit Card Securities
Investment securities
Fair value investments	116.0		151.4
Level 2 Inputs | Collateralized Auto Loans
Investment securities
Fair value investments	167.1		233.2
Level 2 Inputs | Collateralized Securities, Other
Investment securities
Fair value investments	177.3		50.4
Level 2 Inputs | Asset-backed Securities, Securitized Loans and Receivables
Investment securities
Fair value investments	460.4		435.0
Level 2 Inputs | Mortgage-backed and asset-backed securities
Investment securities
Fair value investments	1,788.6		2,073.5
Level 3 Inputs | Government National Mortgage Association Certificates and Obligations (GNMA)
Investment securities
Fair value investments	0		0
Level 3 Inputs | Federal National Mortgage Association Certificates and Obligations (FNMA)
Investment securities
Fair value investments	0		0
Level 3 Inputs | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC)
Investment securities
Fair value investments	0		0
Level 3 Inputs | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Investment securities
Fair value investments	0	[1]	0	[1]
Level 3 Inputs | Residential Mortgage Backed Securities
Investment securities
Fair value investments	24.0		0
Level 3 Inputs | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	0		0
Level 3 Inputs | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	24.0		0
Level 3 Inputs | Collateralized Mortgage Backed Securities
Investment securities
Fair value investments	24.0		0
Level 3 Inputs | Collateralized Credit Card Securities
Investment securities
Fair value investments	22.0		22.1
Level 3 Inputs | Collateralized Auto Loans
Investment securities
Fair value investments	0		0
Level 3 Inputs | Collateralized Securities, Other
Investment securities
Fair value investments	0		0
Level 3 Inputs | Asset-backed Securities, Securitized Loans and Receivables
Investment securities
Fair value investments	22.0		22.1
Level 3 Inputs | Mortgage-backed and asset-backed securities
Investment securities
Fair value investments	46.0		22.1
Fair Value
Investment securities
Fair value investments	6,565.5	[2],[3]	6,950.7	[2],[3]	6,571.9	[4],[5]	7,500.8	[4],[5]
Fair Value | Government National Mortgage Association Certificates and Obligations (GNMA)
Investment securities
Fair value investments	818.0		1,013.4
Fair Value | Federal National Mortgage Association Certificates and Obligations (FNMA)
Investment securities
Fair value investments	52.5		74.6
Fair Value | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC)
Investment securities
Fair value investments	47.8		55.8
Fair Value | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Investment securities
Fair value investments	918.3	[1]	1,143.8	[1]
Fair Value | Residential Mortgage Backed Securities
Investment securities
Fair value investments	133.6		160.6
Fair Value | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	300.3		334.1
Fair Value | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	433.9		494.7
Fair Value | Collateralized Mortgage Backed Securities
Investment securities
Fair value investments	1,352.2		1,638.5
Fair Value | Collateralized Credit Card Securities
Investment securities
Fair value investments	138.0		173.5
Fair Value | Collateralized Auto Loans
Investment securities
Fair value investments	167.1		233.2
Fair Value | Collateralized Securities, Other
Investment securities
Fair value investments	177.3		50.4
Fair Value | Asset-backed Securities, Securitized Loans and Receivables
Investment securities
Fair value investments	482.4		457.1
Fair Value | Mortgage-backed and asset-backed securities
Investment securities
Fair value investments	$ 1,834.6		$ 2,095.6

[1] 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).

[2] Carrying value includes $260.8 that is classified as assets held for sale relating to discontinued operations.

[3] Excludes carrying value of $34.2 associated with other long-term investment limited partnerships accounted for using the equity method and $(0.1) related to forward contracts.

[4] Carrying value includes $111.8 that is classified as assets held for sale relating to discontinued operations.

[5] Excludes carrying value of $33.0 and $34.0 at January 1, 2012 and June 30, 2012 associated with other long-term investment limited partnerships accounted for using the equity method.