Investment Securities (Mortgage-backed Asset Securities) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012		Mar. 31, 2012		Dec. 31, 2011
Level 2 Inputs
Investment securities
Fair value investments	$ 4,795.9		$ 5,206.1		$ 5,115.0		$ 6,088.2
Level 2 Inputs | Government National Mortgage Association Certificates and Obligations (GNMA)
Investment securities
Fair value investments	805.5		1,013.4
Level 2 Inputs | Federal National Mortgage Association Certificates and Obligations (FNMA)
Investment securities
Fair value investments	140.2		74.6
Level 2 Inputs | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC)
Investment securities
Fair value investments	55.6		55.8
Level 2 Inputs | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Investment securities
Fair value investments	1,001.3	[1]	1,143.8	[1]
Level 2 Inputs | Residential Mortgage Backed Securities
Investment securities
Fair value investments	55.6		160.6
Level 2 Inputs | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	276.9		334.1
Level 2 Inputs | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	332.5		494.7
Level 2 Inputs | Collateralized Mortgage Backed Securities
Investment securities
Fair value investments	1,333.8		1,638.5
Level 2 Inputs | Collateralized Credit Card Securities
Investment securities
Fair value investments	110.2		151.4
Level 2 Inputs | Collateralized Auto Loans
Investment securities
Fair value investments	210.3		265.1
Level 2 Inputs | Collateralized Securities, Other
Investment securities
Fair value investments	22.9		18.5
Level 2 Inputs | Asset-backed Securities, Securitized Loans and Receivables
Investment securities
Fair value investments	343.4		435.0
Level 2 Inputs | Mortgage-backed and asset-backed securities
Investment securities
Fair value investments	1,677.2		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	0		0
Level 3 Inputs | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	8.0		0
Level 3 Inputs | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	8.0		0
Level 3 Inputs | Collateralized Mortgage Backed Securities
Investment securities
Fair value investments	8.0		0
Level 3 Inputs | Collateralized Credit Card Securities
Investment securities
Fair value investments	22.1		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	22.1		22.1
Level 3 Inputs | Mortgage-backed and asset-backed securities
Investment securities
Fair value investments	30.1		22.1
Fair Value
Investment securities
Fair value investments	6,580.6	[2],[3]	6,950.7	[2],[3]	6,706.3	[4],[5]	7,500.8	[4],[5]
Fair Value | Government National Mortgage Association Certificates and Obligations (GNMA)
Investment securities
Fair value investments	805.5		1,013.4
Fair Value | Federal National Mortgage Association Certificates and Obligations (FNMA)
Investment securities
Fair value investments	140.2		74.6
Fair Value | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC)
Investment securities
Fair value investments	55.6		55.8
Fair Value | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Investment securities
Fair value investments	1,001.3	[1]	1,143.8	[1]
Fair Value | Residential Mortgage Backed Securities
Investment securities
Fair value investments	55.6		160.6
Fair Value | Commercial Mortgage Backed Securities
Investment securities
Fair value investments	284.9		334.1
Fair Value | Mortgage-backed Securities, Issued by Private Enterprises
Investment securities
Fair value investments	340.5		494.7
Fair Value | Collateralized Mortgage Backed Securities
Investment securities
Fair value investments	1,341.8		1,638.5
Fair Value | Collateralized Credit Card Securities
Investment securities
Fair value investments	132.3		173.5
Fair Value | Collateralized Auto Loans
Investment securities
Fair value investments	210.3		265.1
Fair Value | Collateralized Securities, Other
Investment securities
Fair value investments	22.9		18.5
Fair Value | Asset-backed Securities, Securitized Loans and Receivables
Investment securities
Fair value investments	365.5		457.1
Fair Value | Mortgage-backed and asset-backed securities
Investment securities
Fair value investments	$ 1,707.3		$ 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 $296.9 that is classified as assets held for sale relating to discontinued operations.

[3] Excludes carrying value of $34.9 associated with other long-term investment limited partnerships accounted for using the equity method and $(0.2) related to forward contracts.

[4] Excludes carrying value of $33.0 and $33.2 at March 31, 2012 and January 1, 2012 associated with other long-term investment limited partnerships accounted for using the equity method.

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