Investment Securities (Details 8) (USD $) In Millions, unless otherwise specified																																																																											9 Months Ended				9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012 Level 2	Jun. 30, 2012 Level 2	Mar. 31, 2012 Level 2	Dec. 31, 2011 Level 2	Sep. 30, 2012 Level 3	Jun. 30, 2012 Level 3	Mar. 31, 2012 Level 3	Dec. 31, 2011 Level 3	Sep. 30, 2011 Level 3	Jun. 30, 2011 Level 3	Mar. 31, 2011 Level 3	Dec. 31, 2010 Level 3	Sep. 30, 2012 Asset-backed securities Fair Value	Dec. 31, 2011 Asset-backed securities Fair Value	Sep. 30, 2012 Asset-backed securities Level 2	Dec. 31, 2011 Asset-backed securities Level 2	Sep. 30, 2012 Asset-backed securities Level 3	Dec. 31, 2011 Asset-backed securities Level 3	Sep. 30, 2012 Collateralized debt obligations Fair Value	Dec. 31, 2011 Collateralized debt obligations Fair Value	Sep. 30, 2012 Collateralized debt obligations Level 2	Dec. 31, 2011 Collateralized debt obligations Level 2	Sep. 30, 2012 Collateralized debt obligations Level 3	Dec. 31, 2011 Collateralized debt obligations Level 3	Sep. 30, 2012 Agency commercial mortgage-backed securities Fair Value	Dec. 31, 2011 Agency commercial mortgage-backed securities Fair Value	Sep. 30, 2012 Agency commercial mortgage-backed securities Level 2	Dec. 31, 2011 Agency commercial mortgage-backed securities Level 2	Sep. 30, 2012 GNMA Fair Value	Dec. 31, 2011 GNMA Fair Value	Sep. 30, 2012 GNMA Level 2	Dec. 31, 2011 GNMA Level 2	Sep. 30, 2012 FNMA Fair Value	Dec. 31, 2011 FNMA Fair Value	Sep. 30, 2012 FNMA Level 2	Dec. 31, 2011 FNMA Level 2	Dec. 31, 2011 FHLMC Fair Value	Dec. 31, 2011 FHLMC Level 2	Sep. 30, 2012 Non-agency commercial mortgage-backed securities Fair Value	Dec. 31, 2011 Non-agency commercial mortgage-backed securities Fair Value	Sep. 30, 2012 Non-agency commercial mortgage-backed securities Fair Value Securities issued in 2007	Sep. 30, 2012 Non-agency commercial mortgage-backed securities Fair Value Securities issued in 2009	Sep. 30, 2012 Non-agency commercial mortgage-backed securities Fair Value Securities issued in 2010	Sep. 30, 2012 Non-agency commercial mortgage-backed securities Fair Value Securities issued in 2011	Sep. 30, 2012 Non-agency commercial mortgage-backed securities Fair Value Securities issued in 2012	Sep. 30, 2012 Non-agency commercial mortgage-backed securities Level 2	Dec. 31, 2011 Non-agency commercial mortgage-backed securities Level 2	Sep. 30, 2012 Non-agency commercial mortgage-backed securities Level 3	Dec. 31, 2011 Non-agency commercial mortgage-backed securities Level 3	Sep. 30, 2012 RMBS Fair Value	Dec. 31, 2011 RMBS Fair Value	Sep. 30, 2012 RMBS Fair Value Prime	Sep. 30, 2012 RMBS Fair Value Subprime	Sep. 30, 2012 RMBS Fair Value Senior Tranche Prime	Sep. 30, 2012 RMBS Fair Value Senior Tranche Subprime	Sep. 30, 2012 RMBS Fair Value Securities issued in 2010	Sep. 30, 2012 RMBS Fair Value Securities issued in 2011	Sep. 30, 2012 RMBS Level 2	Dec. 31, 2011 RMBS Level 2	Dec. 31, 2011 RMBS Level 3	Sep. 30, 2012 CMBS Fair Value	Dec. 31, 2011 CMBS Fair Value	Sep. 30, 2012 CMBS Fair Value Super Senior Tranche	Sep. 30, 2012 CMBS Fair Value Senior Tranche	Sep. 30, 2012 CMBS Fair Value Subordinate Tranche	Sep. 30, 2012 CMBS Fair Value Securities issued in 2007	Sep. 30, 2012 CMBS Fair Value Securities issued in 2009	Sep. 30, 2012 CMBS Fair Value Securities issued in 2010	Sep. 30, 2012 CMBS Fair Value Securities issued in 2011	Sep. 30, 2012 CMBS Fair Value Securities issued in 2012	Sep. 30, 2012 CMBS Level 2	Dec. 31, 2011 CMBS Level 2	Sep. 30, 2012 CMBS Level 3	Sep. 30, 2012 CMBS Fixed Rate	Sep. 30, 2012 CMBS Fixed Rate Fair Value	Sep. 30, 2012 CMBS Fixed Rate Fair Value Super Senior Tranche	Sep. 30, 2012 CMBS Fixed Rate Fair Value Senior Tranche	Sep. 30, 2012 CMBS Floating Rate	Sep. 30, 2012 CMBS Floating Rate Fair Value	Sep. 30, 2012 CMBS Floating Rate Fair Value Super Senior Tranche	Sep. 30, 2012 CMBS Floating Rate Fair Value Subordinate Tranche	Sep. 30, 2012 Asset-backed securities Fair Value	Dec. 31, 2011 Asset-backed securities Fair Value	Sep. 30, 2012 Asset-backed securities Level 2	Dec. 31, 2011 Asset-backed securities Level 2	Sep. 30, 2012 Credit card receivables Fair Value	Dec. 31, 2011 Credit card receivables Fair Value	Sep. 30, 2012 Credit card receivables Level 2	Dec. 31, 2011 Credit card receivables Level 2	Sep. 30, 2012 Vehicle receivables Fair Value	Dec. 31, 2011 Vehicle receivables Fair Value	Sep. 30, 2012 Vehicle receivables Level 2	Dec. 31, 2011 Vehicle receivables Level 2	Sep. 30, 2012 Other Fair Value	Sep. 30, 2012 Other Level 2
Investments holding table
Average basis points of subordination																																																																											0.05				0.02
Percentage of underlying loans reported as non-performing	1.00%
Investments at fair value		$ 1,641.7	$ 1,806.4	$ 1,594.6	$ 1,789.0	$ 207.7	$ 219.4	$ 240.9	$ 200.2	$ 255.7	$ 271.4	$ 257.1	$ 289.0	$ 914.0	$ 938.3	$ 912.6	$ 936.0	$ 1.4	$ 2.3	$ 867.1	$ 884.8	$ 865.7	$ 882.5	$ 1.4	$ 2.3	$ 634.3	$ 802.7	$ 634.3	$ 802.7	$ 620.1	$ 631.0	$ 620.1	$ 631.0	$ 14.2	$ 166.8	$ 14.2	$ 166.8	$ 4.9	$ 4.9	$ 232.8	$ 82.1	$ 3.9	$ 4.1	$ 21.1	$ 65.6	$ 138.1	$ 231.4	$ 79.8	$ 1.4	$ 2.3	$ 32.6	$ 13.7	$ 32.6	$ 32.6	$ 32.6	$ 32.6	$ 17.1	$ 15.5	$ 32.6	$ 11.4	$ 2.3	$ 200.2	$ 68.4	$ 151.2	$ 47.6	$ 1.4	$ 3.9	$ 4.1	$ 4.0	$ 50.1	$ 138.1	$ 198.8	$ 68.4	$ 1.4		$ 194.9	$ 147.3	$ 47.6		$ 5.3	$ 3.9	$ 1.4	$ 46.9	$ 53.5	$ 46.9	$ 53.5	$ 25.6	$ 48.2	$ 25.6	$ 48.2	$ 19.8	$ 5.3	$ 19.8	$ 5.3	$ 1.5	$ 1.5