Expected Losses to be Paid (Details 6) (USD $) In Millions, unless otherwise specified							3 Months Ended																				3 Months Ended																																																			3 Months Ended
	Sep. 30, 2013 Close ended second lien		Jun. 30, 2013 Close ended second lien		Dec. 31, 2012 Close ended second lien		Sep. 30, 2013 Total first lien scenario	Sep. 30, 2013 Alt-A first lien		Jun. 30, 2013 Alt-A first lien		Dec. 31, 2012 Alt-A first lien		Sep. 30, 2013 Option ARM		Jun. 30, 2013 Option ARM		Dec. 31, 2012 Option ARM		Sep. 30, 2013 First mortgage, subprime		Jun. 30, 2013 First mortgage, subprime		Dec. 31, 2012 First mortgage, subprime		Sep. 30, 2013 RMBS	Sep. 30, 2013 Prime first lien scenario	Dec. 31, 2012 Prime first lien scenario	Sep. 30, 2013 Minimum Close ended second lien		Jun. 30, 2013 Minimum Close ended second lien		Dec. 31, 2012 Minimum Close ended second lien		Sep. 30, 2013 Minimum Alt-A first lien		Jun. 30, 2013 Minimum Alt-A first lien		Dec. 31, 2012 Minimum Alt-A first lien		Sep. 30, 2013 Minimum Option ARM		Jun. 30, 2013 Minimum Option ARM		Dec. 31, 2012 Minimum Option ARM		Sep. 30, 2013 Minimum First mortgage, subprime		Jun. 30, 2013 Minimum First mortgage, subprime		Dec. 31, 2012 Minimum First mortgage, subprime		Sep. 30, 2013 Maximum Close ended second lien		Jun. 30, 2013 Maximum Close ended second lien		Dec. 31, 2012 Maximum Close ended second lien		Sep. 30, 2013 Maximum Alt-A first lien		Jun. 30, 2013 Maximum Alt-A first lien		Dec. 31, 2012 Maximum Alt-A first lien		Sep. 30, 2013 Maximum Option ARM		Jun. 30, 2013 Maximum Option ARM		Dec. 31, 2012 Maximum Option ARM		Sep. 30, 2013 Maximum First mortgage, subprime		Jun. 30, 2013 Maximum First mortgage, subprime		Dec. 31, 2012 Maximum First mortgage, subprime		Sep. 30, 2013 Somewhat Stressful Environment [Member] Total first lien	Sep. 30, 2013 Somewhat Stressful Environment [Member] Alt-A first lien	Sep. 30, 2013 Somewhat Stressful Environment [Member] Option ARM	Sep. 30, 2013 Somewhat Stressful Environment [Member] First mortgage, subprime	Sep. 30, 2013 Somewhat Stressful Environment [Member] Prime first lien	Sep. 30, 2013 More Stressful Environment [Member] Alt-A first lien	Sep. 30, 2013 More Stressful Environment [Member] Option ARM	Sep. 30, 2013 More Stressful Environment [Member] First mortgage, subprime	Sep. 30, 2013 More Stressful Environment [Member] Prime first lien	Sep. 30, 2013 Somewhat Less Stressful Environment [Member] Total first lien	Sep. 30, 2013 Somewhat Less Stressful Environment [Member] Alt-A first lien	Sep. 30, 2013 Somewhat Less Stressful Environment [Member] Option ARM	Sep. 30, 2013 Somewhat Less Stressful Environment [Member] First mortgage, subprime	Sep. 30, 2013 Somewhat Less Stressful Environment [Member] Prime first lien	Sep. 30, 2013 Least Stressful Environment [Member] Alt-A first lien	Sep. 30, 2013 Least Stressful Environment [Member] Option ARM	Sep. 30, 2013 Least Stressful Environment [Member] First mortgage, subprime	Sep. 30, 2013 Least Stressful Environment [Member] Prime first lien
Guarantor Obligations [Line Items]
Plateau conditional default rate (as a percent)																													6.20%	[1]	7.30%	[1]	7.30%	[1]	3.40%	[1]	3.70%	[1]	3.80%	[1]	6.40%	[1]	5.60%	[1]	7.00%	[1]	6.50%	[1]	6.70%	[1]	7.30%	[1]	14.40%	[1]	15.80%	[1]	20.70%	[1]	22.10%	[1]	22.30%	[1]	23.20%	[1]	24.70%	[1]	24.20%	[1]	26.10%	[1]	23.70%	[1]	24.70%	[1]	26.20%	[1]
Intermediate Conditional Default Rate																										5.00%									0.70%	[1]	0.70%	[1]	0.80%	[1]	1.30%	[1]	1.10%	[1]	1.40%	[1]	1.30%	[1]	1.30%	[1]	1.50%	[1]							4.40%	[1]	4.50%	[1]	4.60%	[1]	4.90%	[1]	4.80%	[1]	5.20%	[1]	4.70%	[1]	4.90%	[1]	5.20%	[1]
Final conditional default rate trended down to (as a percent)																													3.50%	[1]	3.50%	[1]	3.50%	[1]	0.20%	[1]	0.20%	[1]	0.20%	[1]	0.30%	[1]	0.30%	[1]	0.40%	[1]	0.30%	[1]	0.30%	[1]	0.40%	[1]	9.10%	[1]	9.10%	[1]	9.10%	[1]	1.10%	[1]	1.10%	[1]	1.20%	[1]	1.20%	[1]	1.20%	[1]	1.30%	[1]	1.20%	[1]	1.20%	[1]	1.30%	[1]
Loss severity (as a percent)	98.00%	[1]	98.00%	[1]	98.00%	[1]		65.00%	[1]	65.00%	[1]	65.00%	[1]	65.00%	[1]	65.00%	[1]	65.00%	[1]	90.00%	[1]	90.00%	[1]	90.00%	[1]
Initial conditional prepayment rate (as a percent)																													3.00%	[1]	1.70%	[1]	1.90%	[1]	0.00%	[1]	0.40%	[1]	0.00%	[1]	0.20%	[1]	0.30%	[1]	0.00%	[1]	0.00%	[1]	0.00%	[1]	0.00%	[1]	13.00%	[1]	14.00%	[1]	12.50%	[1]	39.50%	[1]	32.20%	[1]	39.40%	[1]	10.90%	[1]	7.70%	[1]	10.70%	[1]	11.80%	[1]	14.80%	[1]	17.60%	[1]
Final conditional prepayment rate (as a percent)	10.00%	[1]	10.00%	[1]	10.00%	[1]		15.00%	[1]	15.00%	[1]	15.00%	[1]	15.00%	[1]	15.00%	[1]	15.00%	[1]	15.00%	[1]	15.00%	[1]	15.00%	[1]
Period from initial to final conditional prepayment rate (in months)							12 months																																																																															12 months
Current conditional prepayment rate used in alternate scenario for loss estimate (as a percent)							15.00%
Number of scenarios weighted in estimating expected losses																											5	5
Increase in the plateau period used to calculate potential change in loss estimate (in months)																																																																																	3 months
Increased plateau period used to calculate potential change in loss estimate (in months)																																																																																	27 months
Prior loss severity recovery period used to calculate potential change in loss estimate (in years)																																																																																	4 years
Current loss severity recovery period used to calculate potential change in loss estimate (in years)																																																																																	2 years					2 years
Increased final loss severity for subprime transactions used to calculate potential change in loss estimate (as a percent)																																																																													60.00%
Increase in expected loss in case of increase in conditional default rate plateau period and loss severity recovery period																																																																														$ 60	$ 17	$ 100	$ 4
Loss severity recovery period used to calculate potential change in loss estimate in even more stressful scenario (in years)							8 years
Period of decrease in conditional default rate until final rate is achieved (in months)																																																																																					15 months									9 months
Increase in expected loss in case of increase in loss severity recovery period in an even more stressful scenario																																																																																		165	42	158	13
Number of scenarios where the recovery was faster than in base case							2
Initial subprime loss severity rate assumed for 12 months (as a percent)																																																																																						80.00%
Initial subprime loss severity rate assumed to be recovered over two years (as a percent)																																																																																						40.00%
Decrease in expected loss in case of less gradual conditional default rate recovery and changes in initial subprime loss severity rate																																																																																							6	12	28	1
Decrease in the plateau period used to calculate potential change in loss estimate (in months)							3 months
Decreased plateau period used to calculate potential change in loss estimate (in months)							21 months
Decrease in expected loss in case of decrease in conditional default rate plateau period																																																																																											$ 60	$ 36	$ 81	$ 5

[1] Represents variables for most heavily weighted scenario (the “base case”).