Investment Securities (Details 7) (USD $) In Millions, unless otherwise specified																																																																													12 Months Ended				12 Months Ended
	Dec. 31, 2011 Fair Value	Dec. 31, 2010 Fair Value	Dec. 31, 2011 Level 2 Inputs	Dec. 31, 2010 Level 2 Inputs	Dec. 31, 2011 Mortgage-backed and asset-backed securities Fair Value	Dec. 31, 2010 Mortgage-backed and asset-backed securities Fair Value	Dec. 31, 2011 Mortgage-backed and asset-backed securities Level 2 Inputs	Dec. 31, 2010 Mortgage-backed and asset-backed securities Level 2 Inputs	Dec. 31, 2011 Mortgage-backed and asset-backed securities Level 3 Inputs	Dec. 31, 2010 Mortgage-backed and asset-backed securities Level 3 Inputs	Dec. 31, 2011 Mortgage-backed securities Fair Value	Dec. 31, 2010 Mortgage-backed securities Fair Value	Dec. 31, 2011 Mortgage-backed securities Level 2 Inputs	Dec. 31, 2010 Mortgage-backed securities Level 2 Inputs	Dec. 31, 2011 Mortgage-backed securities Level 3 Inputs	Dec. 31, 2010 Mortgage-backed securities Level 3 Inputs	Dec. 31, 2011 Agency mortgage-backed securities Fair Value	Dec. 31, 2010 Agency mortgage-backed securities Fair Value	Dec. 31, 2011 Agency mortgage-backed securities Level 2 Inputs	Dec. 31, 2010 Agency mortgage-backed securities Level 2 Inputs	Dec. 31, 2010 Agency mortgage-backed securities Level 3 Inputs	Dec. 31, 2011 GNMA Fair Value	Dec. 31, 2010 GNMA Fair Value	Dec. 31, 2011 GNMA Level 2 Inputs	Dec. 31, 2010 GNMA Level 2 Inputs	Dec. 31, 2010 GNMA Level 3 Inputs	Dec. 31, 2011 FNMA Fair Value	Dec. 31, 2010 FNMA Fair Value	Dec. 31, 2011 FNMA Level 2 Inputs	Dec. 31, 2010 FNMA Level 2 Inputs	Dec. 31, 2011 FHLMC Fair Value	Dec. 31, 2010 FHLMC Fair Value	Dec. 31, 2011 FHLMC Level 2 Inputs	Dec. 31, 2010 FHLMC Level 2 Inputs	Dec. 31, 2011 Non-agency mortgage-backed securities 2003	Dec. 31, 2011 Non-agency mortgage-backed securities 2006	Dec. 31, 2011 Non-agency mortgage-backed securities 2007	Dec. 31, 2011 Non-agency mortgage-backed securities 2009	Dec. 31, 2011 Non-agency mortgage-backed securities 2010	Dec. 31, 2011 Non-agency mortgage-backed securities 2011	Dec. 31, 2011 Non-agency mortgage-backed securities Fair Value	Dec. 31, 2010 Non-agency mortgage-backed securities Fair Value	Dec. 31, 2011 Non-agency mortgage-backed securities Level 2 Inputs	Dec. 31, 2010 Non-agency mortgage-backed securities Level 2 Inputs	Dec. 31, 2011 Non-agency mortgage-backed securities Level 3 Inputs	Dec. 31, 2010 Non-agency mortgage-backed securities Level 3 Inputs	Dec. 31, 2011 Non-agency residential mortgage-backed securities (RMBS) Super Senior	Dec. 31, 2011 Non-agency residential mortgage-backed securities (RMBS) Super Senior Prime	Dec. 31, 2011 Non-agency residential mortgage-backed securities (RMBS) Super Senior Non-prime	Dec. 31, 2011 Non-agency residential mortgage-backed securities (RMBS) Senior	Dec. 31, 2011 Non-agency residential mortgage-backed securities (RMBS) Senior Prime	Dec. 31, 2011 Non-agency residential mortgage-backed securities (RMBS) Senior Non-prime	Dec. 31, 2011 Non-agency residential mortgage-backed securities (RMBS) 2003	Dec. 31, 2011 Non-agency residential mortgage-backed securities (RMBS) 2006	Dec. 31, 2011 Non-agency residential mortgage-backed securities (RMBS) 2007	Dec. 31, 2011 Non-agency residential mortgage-backed securities (RMBS) 2010	Dec. 31, 2011 Non-agency residential mortgage-backed securities (RMBS) 2011	Dec. 31, 2011 Non-agency residential mortgage-backed securities (RMBS) Fair Value	Dec. 31, 2010 Non-agency residential mortgage-backed securities (RMBS) Fair Value	Dec. 31, 2011 Non-agency residential mortgage-backed securities (RMBS) Fair Value Prime	Dec. 31, 2011 Non-agency residential mortgage-backed securities (RMBS) Fair Value Non-prime	Dec. 31, 2011 Non-agency residential mortgage-backed securities (RMBS) Level 2 Inputs	Dec. 31, 2010 Non-agency residential mortgage-backed securities (RMBS) Level 2 Inputs	Dec. 31, 2011 Non-agency residential mortgage-backed securities (RMBS) Level 3 Inputs	Dec. 31, 2010 Non-agency residential mortgage-backed securities (RMBS) Level 3 Inputs	Dec. 31, 2011 Non-agency commercial mortgage-backed securities (CMBS) Super Senior	Dec. 31, 2011 Non-agency commercial mortgage-backed securities (CMBS) Senior	Dec. 31, 2011 Non-agency commercial mortgage-backed securities (CMBS) 2007	Dec. 31, 2011 Non-agency commercial mortgage-backed securities (CMBS) 2009	Dec. 31, 2011 Non-agency commercial mortgage-backed securities (CMBS) 2010	Dec. 31, 2011 Non-agency commercial mortgage-backed securities (CMBS) 2011	Dec. 31, 2011 Non-agency commercial mortgage-backed securities (CMBS) Fair Value	Dec. 31, 2010 Non-agency commercial mortgage-backed securities (CMBS) Fair Value	Dec. 31, 2011 Non-agency commercial mortgage-backed securities (CMBS) Level 2 Inputs	Dec. 31, 2010 Non-agency commercial mortgage-backed securities (CMBS) Level 2 Inputs	Dec. 31, 2011 Non-agency commercial mortgage-backed securities (CMBS) Maximum	Dec. 31, 2011 Fixed Rate CMBS	Dec. 31, 2011 Fixed Rate CMBS Super Senior	Dec. 31, 2011 Fixed Rate CMBS Senior	Dec. 31, 2011 Fixed Rate CMBS Fair Value	Dec. 31, 2011 Floating Rate CMBS	Dec. 31, 2011 Floating Rate CMBS Super Senior	Dec. 31, 2011 Floating Rate CMBS Senior	Dec. 31, 2011 Floating Rate CMBS Fair Value	Dec. 31, 2011 Other asset-backed securities Fair Value	Dec. 31, 2010 Other asset-backed securities Fair Value	Dec. 31, 2011 Other asset-backed securities Level 2 Inputs	Dec. 31, 2010 Other asset-backed securities Level 2 Inputs	Dec. 31, 2011 Credit card receivables Fair Value	Dec. 31, 2010 Credit card receivables Fair Value	Dec. 31, 2011 Credit card receivables Level 2 Inputs	Dec. 31, 2010 Credit card receivables Level 2 Inputs	Dec. 31, 2011 Vehicle receivables Fair Value	Dec. 31, 2010 Vehicle receivables Fair Value	Dec. 31, 2011 Vehicle receivables Level 2 Inputs	Dec. 31, 2010 Vehicle receivables Level 2 Inputs	Dec. 31, 2011 Other Fair Value	Dec. 31, 2010 Other Fair Value	Dec. 31, 2011 Other Level 2 Inputs	Dec. 31, 2010 Other Level 2 Inputs
Mortgage-backed, Asset-backed Securities Abstract
Average basis points of subordination (as a percent)																																																																													20				45
Percentage of underlying loans reported as non-performing																																																																												2.00%
Fair value investments	$ 8,346.8	$ 7,901.6	$ 6,088.2	$ 5,477.4	$ 3,222.9	$ 2,071.7	$ 3,207.8	$ 2,014.7	$ 15.1	$ 57.0	$ 2,474.1	$ 1,595.2	$ 2,459.0	$ 1,538.2	$ 15.1	$ 57.0	$ 2,114.3	$ 1,417.6	$ 2,114.3	$ 1,376.7	$ 40.9	$ 1,365.8	$ 1,143.6	$ 1,365.8	$ 1,102.7	$ 40.9	$ 712.6	$ 234.9	$ 712.6	$ 234.9	$ 35.9	$ 39.1	$ 35.9	$ 39.1	$ 3.3	$ 23.0	$ 43.8	$ 11.2	$ 12.8	$ 265.7	$ 359.8	$ 177.6	$ 344.7	$ 161.5	$ 15.1	$ 16.1	$ 35.7	$ 20.5	$ 15.2	$ 47.4	$ 46.7	$ 0.7	$ 3.3	$ 23.0	$ 26.4	$ 10.5	$ 19.9	$ 83.1	$ 90.6	$ 67.2	$ 15.9	$ 68.0	$ 74.5	$ 15.1	$ 16.1	$ 64.1	$ 212.6	$ 17.4	$ 11.2	$ 2.3	$ 245.8	$ 276.7	$ 87.0	$ 276.7	$ 87.0			$ 46.7	$ 202.6	$ 249.3		$ 17.4	$ 10.0	$ 27.4	$ 748.8	$ 476.5	$ 748.8	$ 476.5	$ 380.6	$ 248.3	$ 380.6	$ 248.3	$ 345.6	$ 228.1	$ 345.6	$ 228.1	$ 22.6	$ 0.1	$ 22.6	$ 0.1