Investment Securities (Details 8) (USD $) In Millions, unless otherwise specified																																																																										6 Months Ended				6 Months Ended
	Jun. 30, 2011 Mortgage-backed and asset-backed securities Fair Value	Dec. 31, 2010 Mortgage-backed and asset-backed securities Fair Value	Jun. 30, 2011 Mortgage-backed and asset-backed securities Level 3 Inputs	Dec. 31, 2010 Mortgage-backed and asset-backed securities Level 3 Inputs	Jun. 30, 2011 Mortgage-backed and asset-backed securities Level 2 Inputs	Dec. 31, 2010 Mortgage-backed and asset-backed securities Level 2 Inputs	Jun. 30, 2011 Mortgage-backed securities Fair Value	Dec. 31, 2010 Mortgage-backed securities Fair Value	Jun. 30, 2011 Mortgage-backed securities Level 2 Inputs	Dec. 31, 2010 Mortgage-backed securities Level 2 Inputs	Jun. 30, 2011 Level 3 Inputs Mortgage-backed securities	Dec. 31, 2010 Level 3 Inputs Mortgage-backed securities	Jun. 30, 2011 Agency mortgage-backed securities Fair Value	Dec. 31, 2010 Agency mortgage-backed securities Fair Value	Jun. 30, 2011 Agency mortgage-backed securities Level 2 Inputs	Dec. 31, 2010 Agency mortgage-backed securities Level 2 Inputs	Jun. 30, 2011 Level 3 Inputs Agency mortgage-backed securities	Dec. 31, 2010 Level 3 Inputs Agency mortgage-backed securities	Jun. 30, 2011 GNMA Fair Value	Dec. 31, 2010 GNMA Fair Value	Jun. 30, 2011 GNMA Level 2 Inputs	Dec. 31, 2010 GNMA Level 2 Inputs	Jun. 30, 2011 Level 3 Inputs GNMA	Dec. 31, 2010 Level 3 Inputs GNMA	Jun. 30, 2011 FNMA Fair Value	Dec. 31, 2010 FNMA Fair Value	Jun. 30, 2011 FNMA Level 2 Inputs	Dec. 31, 2010 FNMA Level 2 Inputs	Jun. 30, 2011 Level 3 Inputs FNMA	Jun. 30, 2011 FHLMC Fair Value	Dec. 31, 2010 FHLMC Fair Value	Jun. 30, 2011 FHLMC Level 2 Inputs	Dec. 31, 2010 FHLMC Level 2 Inputs	Jun. 30, 2011 Non-agency mortgage-backed securities 2003	Jun. 30, 2011 Non-agency mortgage-backed securities 2005	Jun. 30, 2011 Non-agency mortgage-backed securities 2006	Jun. 30, 2011 Non-agency mortgage-backed securities 2007	Jun. 30, 2011 Non-agency mortgage-backed securities 2010	Jun. 30, 2011 Non-agency mortgage-backed securities 2011	Jun. 30, 2011 Non-agency mortgage-backed securities Fair Value	Dec. 31, 2010 Non-agency mortgage-backed securities Fair Value	Jun. 30, 2011 Non-agency mortgage-backed securities Level 2 Inputs	Dec. 31, 2010 Non-agency mortgage-backed securities Level 2 Inputs	Dec. 31, 2010 Level 3 Inputs Non-agency mortgage-backed securities	Jun. 30, 2011 Non-agency residential mortgage-backed securities (RMBS) 2003	Jun. 30, 2011 Non-agency residential mortgage-backed securities (RMBS) 2006	Jun. 30, 2011 Non-agency residential mortgage-backed securities (RMBS) 2007	Jun. 30, 2011 Non-agency residential mortgage-backed securities (RMBS) 2010	Jun. 30, 2011 Non-agency residential mortgage-backed securities (RMBS) 2011	Jun. 30, 2011 Non-agency residential mortgage-backed securities (RMBS) Fair Value	Dec. 31, 2010 Non-agency residential mortgage-backed securities (RMBS) Fair Value	Jun. 30, 2011 Non-agency residential mortgage-backed securities (RMBS) Fair Value Prime	Jun. 30, 2011 Non-agency residential mortgage-backed securities (RMBS) Fair Value Non-prime	Jun. 30, 2011 Non-agency residential mortgage-backed securities (RMBS) Level 2 Inputs	Dec. 31, 2010 Non-agency residential mortgage-backed securities (RMBS) Level 2 Inputs	Jun. 30, 2011 Non-agency residential mortgage-backed securities (RMBS) Super Senior	Jun. 30, 2011 Non-agency residential mortgage-backed securities (RMBS) Super Senior Prime	Jun. 30, 2011 Non-agency residential mortgage-backed securities (RMBS) Super Senior Non-prime	Jun. 30, 2011 Non-agency residential mortgage-backed securities (RMBS) Senior	Jun. 30, 2011 Non-agency residential mortgage-backed securities (RMBS) Senior Prime	Jun. 30, 2011 Non-agency residential mortgage-backed securities (RMBS) Senior Non-prime	Dec. 31, 2010 Level 3 Inputs Non-agency residential mortgage-backed securities (RMBS)	Jun. 30, 2011 Non-agency commercial mortgage-backed securities (CMBS)	Jun. 30, 2011 Non-agency commercial mortgage-backed securities (CMBS) 2003	Jun. 30, 2011 Non-agency commercial mortgage-backed securities (CMBS) 2005	Jun. 30, 2011 Non-agency commercial mortgage-backed securities (CMBS) 2007	Jun. 30, 2011 Non-agency commercial mortgage-backed securities (CMBS) 2011	Jun. 30, 2011 Non-agency commercial mortgage-backed securities (CMBS) Fair Value	Dec. 31, 2010 Non-agency commercial mortgage-backed securities (CMBS) Fair Value	Jun. 30, 2011 Non-agency commercial mortgage-backed securities (CMBS) Level 2 Inputs	Dec. 31, 2010 Non-agency commercial mortgage-backed securities (CMBS) Level 2 Inputs	Jun. 30, 2011 Non-agency commercial mortgage-backed securities (CMBS) Super Senior	Jun. 30, 2011 Non-agency commercial mortgage-backed securities (CMBS) Senior	Jun. 30, 2011 Fixed Rate CMBS	Jun. 30, 2011 Fixed Rate CMBS Fair Value	Jun. 30, 2011 Fixed Rate CMBS Super Senior	Jun. 30, 2011 Fixed Rate CMBS Senior	Jun. 30, 2011 Floating Rate CMBS	Jun. 30, 2011 Floating Rate CMBS Fair Value	Jun. 30, 2011 Floating Rate CMBS Super Senior	Jun. 30, 2011 Other asset-backed securities Fair Value	Dec. 31, 2010 Other asset-backed securities Fair Value	Jun. 30, 2011 Other asset-backed securities Level 2 Inputs	Dec. 31, 2010 Other asset-backed securities Level 2 Inputs	Jun. 30, 2011 Credit card receivables Fair Value	Dec. 31, 2010 Credit card receivables Fair Value	Jun. 30, 2011 Credit card receivables Level 2 Inputs	Dec. 31, 2010 Credit card receivables Level 2 Inputs	Jun. 30, 2011 Vehicle receivables Fair Value	Dec. 31, 2010 Vehicle receivables Fair Value	Jun. 30, 2011 Vehicle receivables Level 2 Inputs	Dec. 31, 2010 Vehicle receivables Level 2 Inputs	Jun. 30, 2011 Other Fair Value	Dec. 31, 2010 Other Fair Value	Jun. 30, 2011 Other Level 2 Inputs	Dec. 31, 2010 Other Level 2 Inputs	Jun. 30, 2011 Fair Value	Dec. 31, 2010 Fair Value	Jun. 30, 2011 Level 2 Inputs	Dec. 31, 2010 Level 2 Inputs
Mortgage-backed, Asset-backed Securities Abstract
Average basis points of subordination (as a percent)																																																																										20				60
Percentage of underlying loans reported as non-performing (as a percent)																																																															1.00%
Fair value investments	$ 2,308.0	$ 2,071.7	$ 52.8	$ 57.0	$ 2,255.2	$ 2,014.7	$ 1,774.2	$ 1,595.2	$ 1,721.4	$ 1,538.2	$ 52.8	$ 57.0	$ 1,554.7	$ 1,417.6	$ 1,501.9	$ 1,376.7	$ 52.8	$ 40.9	$ 1,222.8	$ 1,143.6	$ 1,170.7	$ 1,102.7	$ 52.1	$ 40.9	$ 264.4	$ 234.9	$ 263.7	$ 234.9	$ 0.7	$ 67.5	$ 39.1	$ 67.5	$ 39.1	$ 6.8	$ 22.8	$ 42.6	$ 46.0	$ 10.5	$ 90.8	$ 219.5	$ 177.6	$ 219.5	$ 161.5	$ 16.1	$ 3.8	$ 42.6	$ 29.6	$ 10.5	$ 21.6	$ 108.1	$ 90.6	$ 90.1	$ 18.0	$ 108.1	$ 74.5	$ 44.3	$ 27.2	$ 17.1	$ 63.8	$ 62.9	$ 0.9	$ 16.1		$ 3.0	$ 22.8	$ 16.4	$ 69.2	$ 111.4	$ 87.0	$ 111.4	$ 87.0	$ 39.3	$ 72.1		$ 80.5	$ 8.4	$ 72.1		$ 30.9	$ 30.9	$ 533.8	$ 476.5	$ 533.8	$ 476.5	$ 223.7	$ 248.3	$ 223.7	$ 248.3	$ 285.8	$ 228.1	$ 285.8	$ 228.1	$ 24.3	$ 0.1	$ 24.3	$ 0.1	$ 7,493.9	$ 7,901.6	$ 5,330.6	$ 5,477.4