Investment Securities (Mortgage-backed Asset Securities) (Details) (USD $)	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Level 2 Inputs
Investment securities
Fair value investments	$ 5,206,100,000		$ 6,088,200,000		$ 5,477,400,000
Level 2 Inputs | GNMA
Investment securities
Fair value investments	1,013,400,000		1,365,800,000
Level 2 Inputs | FNMA
Investment securities
Fair value investments	74,600,000		712,600,000
Level 2 Inputs | FHLMC
Investment securities
Fair value investments	55,800,000		35,900,000
Level 2 Inputs | Total Agency
Investment securities
Fair value investments	1,143,800,000	[1]	2,114,300,000	[1]
Level 2 Inputs | Residential
Investment securities
Fair value investments	160,600,000		68,000,000
Level 2 Inputs | Commercial
Investment securities
Fair value investments	334,100,000		276,700,000
Level 2 Inputs | Total Non-agency
Investment securities
Fair value investments	494,700,000		344,700,000
Level 2 Inputs | Total mortgage-backed securities
Investment securities
Fair value investments	1,638,500,000		2,459,000,000
Level 2 Inputs | Credit card receivables
Investment securities
Fair value investments	151,400,000		380,600,000
Level 2 Inputs | Vehicle receivables
Investment securities
Fair value investments	265,100,000		345,600,000
Level 2 Inputs | Other
Investment securities
Fair value investments	18,500,000		22,600,000
Level 2 Inputs | Total other asset-backed securities
Investment securities
Fair value investments	435,000,000		748,800,000
Level 2 Inputs | Total mortgage and asset- backed securities
Investment securities
Fair value investments	2,073,500,000		3,207,800,000
Level 3 Inputs | GNMA
Investment securities
Fair value investments	0		0
Level 3 Inputs | FNMA
Investment securities
Fair value investments	0		0
Level 3 Inputs | FHLMC
Investment securities
Fair value investments	0		0
Level 3 Inputs | Total Agency
Investment securities
Fair value investments	0	[1]	0	[1]
Level 3 Inputs | Residential
Investment securities
Fair value investments	0		15,100,000
Level 3 Inputs | Commercial
Investment securities
Fair value investments	0		0
Level 3 Inputs | Total Non-agency
Investment securities
Fair value investments	0		15,100,000
Level 3 Inputs | Total mortgage-backed securities
Investment securities
Fair value investments	0		15,100,000
Level 3 Inputs | Credit card receivables
Investment securities
Fair value investments	22,100,000		0
Level 3 Inputs | Vehicle receivables
Investment securities
Fair value investments	0		0
Level 3 Inputs | Other
Investment securities
Fair value investments	0		0
Level 3 Inputs | Total other asset-backed securities
Investment securities
Fair value investments	22,100,000		0
Level 3 Inputs | Total mortgage and asset- backed securities
Investment securities
Fair value investments	22,100,000		15,100,000
Fair value
Investment securities
Fair value investments	7,581,300,000	[2],[3]	8,346,800,000	[2],[3],[4],[5]	7,901,600,000	[4]
Fair value | GNMA
Investment securities
Fair value investments	1,013,400,000		1,365,800,000
Fair value | FNMA
Investment securities
Fair value investments	74,600,000		712,600,000
Fair value | FHLMC
Investment securities
Fair value investments	55,800,000		35,900,000
Fair value | Total Agency
Investment securities
Fair value investments	1,143,800,000	[1]	2,114,300,000	[1]
Fair value | Residential
Investment securities
Fair value investments	160,600,000		83,100,000
Fair value | Commercial
Investment securities
Fair value investments	334,100,000		276,700,000
Fair value | Total Non-agency
Investment securities
Fair value investments	494,700,000		359,800,000
Fair value | Total mortgage-backed securities
Investment securities
Fair value investments	1,638,500,000		2,474,100,000
Fair value | Credit card receivables
Investment securities
Fair value investments	173,500,000		380,600,000
Fair value | Vehicle receivables
Investment securities
Fair value investments	265,100,000		345,600,000
Fair value | Other
Investment securities
Fair value investments	18,500,000		22,600,000
Fair value | Total other asset-backed securities
Investment securities
Fair value investments	457,100,000		748,800,000
Fair value | Total mortgage and asset- backed securities
Investment securities
Fair value investments	$ 2,095,600,000		$ 3,222,900,000

[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] Excludes carrying value of $33.0 and $35.0 at January 1, 2012 and December 31, 2012 associated with other long-term investments accounted for using the equity method and $(0.1) at December 31, 2012 related to currency forward contracts.

[3] Carrying value includes $111.8 and $338.1 at January 1, 2012 and December 31, 2012 that is classified as assets held for sale relating to discontinued operations.

[4] Excludes carrying value of $33.0 and $41.9 at December 31, 2011 and January 1, 2011 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 AutoOne discontinued operations.