Expected Losses to be Paid (Details 5) (USD $) In Millions, unless otherwise specified	3 Months Ended																			3 Months Ended	9 Months Ended			9 Months Ended		3 Months Ended																		3 Months Ended																																																						3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended			12 Months Ended	3 Months Ended
	Sep. 30, 2013	Sep. 30, 2013 Alt-A first lien		Jun. 30, 2013 Alt-A first lien		Dec. 31, 2012 Alt-A first lien		Sep. 30, 2013 Alt-A first lien Minimum		Jun. 30, 2013 Alt-A first lien Minimum		Dec. 31, 2012 Alt-A first lien Minimum		Sep. 30, 2013 Alt-A first lien Maximum		Jun. 30, 2013 Alt-A first lien Maximum		Dec. 31, 2012 Alt-A first lien Maximum		Sep. 30, 2013 Second lien Curve	Sep. 30, 2013 Second lien	Jun. 30, 2013 Second lien	Dec. 31, 2012 Second lien	Sep. 30, 2013 Second lien Minimum	Sep. 30, 2013 Second lien Maximum	Sep. 30, 2013 Close ended second lien		Jun. 30, 2013 Close ended second lien		Dec. 31, 2012 Close ended second lien		Sep. 30, 2013 Close ended second lien Minimum		Jun. 30, 2013 Close ended second lien Minimum		Dec. 31, 2012 Close ended second lien Minimum		Sep. 30, 2013 Close ended second lien Maximum		Jun. 30, 2013 Close ended second lien Maximum		Dec. 31, 2012 Close ended second lien Maximum		Sep. 30, 2013 HELOCs		Jun. 30, 2013 HELOCs		Dec. 31, 2012 HELOCs		Sep. 30, 2013 HELOCs Minimum		Jun. 30, 2013 HELOCs Minimum		Dec. 31, 2012 HELOCs Minimum		Sep. 30, 2013 HELOCs Maximum		Jun. 30, 2013 HELOCs Maximum		Dec. 31, 2012 HELOCs Maximum		Sep. 30, 2013 Option ARM		Jun. 30, 2013 Option ARM		Dec. 31, 2012 Option ARM		Sep. 30, 2013 Option ARM Minimum		Jun. 30, 2013 Option ARM Minimum		Dec. 31, 2012 Option ARM Minimum		Sep. 30, 2013 Option ARM Maximum		Jun. 30, 2013 Option ARM Maximum		Dec. 31, 2012 Option ARM Maximum		Sep. 30, 2013 Residential, Subprime, Financing Receivable [Member]		Jun. 30, 2013 Residential, Subprime, Financing Receivable [Member]		Dec. 31, 2012 Residential, Subprime, Financing Receivable [Member]		Sep. 30, 2013 Residential, Subprime, Financing Receivable [Member] Minimum		Jun. 30, 2013 Residential, Subprime, Financing Receivable [Member] Minimum		Dec. 31, 2012 Residential, Subprime, Financing Receivable [Member] Minimum		Sep. 30, 2013 Residential, Subprime, Financing Receivable [Member] Maximum		Jun. 30, 2013 Residential, Subprime, Financing Receivable [Member] Maximum		Dec. 31, 2012 Residential, Subprime, Financing Receivable [Member] Maximum		Sep. 30, 2013 Base Scenario Second lien	Dec. 31, 2012 Base Scenario Second lien	Sep. 30, 2013 Scenario 1 Second lien	Dec. 31, 2012 Scenario 1 Second lien	Sep. 30, 2013 Scenario 1 Close ended second lien	Sep. 30, 2013 Scenario 1 HELOCs	Sep. 30, 2013 Scenario 2 Second lien	Dec. 31, 2012 Scenario 2 Second lien	Sep. 30, 2013 Scenario 2 Close ended second lien	Sep. 30, 2013 Scenario 2 HELOCs
Guarantor Obligations [Line Items]
Plateau conditional default rate (as a percent)								3.40%	[1]	3.70%	[1]	3.80%	[1]	22.10%	[1]	22.30%	[1]	23.20%	[1]													6.20%	[1]	7.30%	[1]	7.30%	[1]	14.40%	[1]	15.80%	[1]	20.70%	[1]							1.40%	[1]	3.40%	[1]	3.80%	[1]	8.90%	[1]	9.80%	[1]	15.90%	[1]							6.40%	[1]	5.60%	[1]	7.00%	[1]	24.70%	[1]	24.20%	[1]	26.10%	[1]							6.50%	[1]	6.70%	[1]	7.30%	[1]	23.70%	[1]	24.70%	[1]	26.20%	[1]
Intermediate Conditional Default Rate								0.70%	[1]	0.70%	[1]	0.80%	[1]	4.40%	[1]	4.50%	[1]	4.60%	[1]																																																	1.30%	[1]	1.10%	[1]	1.40%	[1]	4.90%	[1]	4.80%	[1]	5.20%	[1]							1.30%	[1]	1.30%	[1]	1.50%	[1]	4.70%	[1]	4.90%	[1]	5.20%	[1]
Final conditional default rate trended down to (as a percent)								0.20%	[1]	0.20%	[1]	0.20%	[1]	1.10%	[1]	1.10%	[1]	1.20%	[1]													3.50%	[1]	3.50%	[1]	3.50%	[1]	9.10%	[1]	9.10%	[1]	9.10%	[1]							0.40%	[1]	0.40%	[1]	0.40%	[1]	3.20%	[1]	3.20%	[1]	3.20%	[1]							0.30%	[1]	0.30%	[1]	0.40%	[1]	1.20%	[1]	1.20%	[1]	1.30%	[1]							0.30%	[1]	0.30%	[1]	0.40%	[1]	1.20%	[1]	1.20%	[1]	1.30%	[1]
Loss severity (as a percent)		65.00%	[1]	65.00%	[1]	65.00%	[1]																			98.00%	[1]	98.00%	[1]	98.00%	[1]													98.00%	[1]	98.00%	[1]	98.00%	[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)								0.00%	[1]	0.40%	[1]	0.00%	[1]	39.50%	[1]	32.20%	[1]	39.40%	[1]													3.00%	[1]	1.70%	[1]	1.90%	[1]	13.00%	[1]	14.00%	[1]	12.50%	[1]							4.50%	[1]	2.10%	[1]	2.90%	[1]	20.00%	[1]	20.10%	[1]	15.40%	[1]							0.20%	[1]	0.30%	[1]	0.00%	[1]	10.90%	[1]	7.70%	[1]	10.70%	[1]							0.00%	[1]	0.00%	[1]	0.00%	[1]	11.80%	[1]	14.80%	[1]	17.60%	[1]
Final conditional prepayment rate (as a percent)		15.00%	[1]	15.00%	[1]	15.00%	[1]													10.00%	10.00%					10.00%	[1]	10.00%	[1]	10.00%	[1]													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]
Expected period until final conditional default rate (in months)																										34 months	[1]	34 months	[1]	36 months														34 months		34 months		36 months	[1]
Typical past due period for loans to be charged off (in days)																					180 days
First delinquency category (in days)																								30 days	59 days
Second delinquency category (in days)																								60 days	89 days
Third delinquency category (in days)																								90 days	119 days
Fourth delinquency category (in days)																								120 days	149 days
Fifth delinquency category (in days)																								150 days	179 days
Period of Default Estimate																					5 months
Number of Preceding Months Liquidation Rates Used to Estimate Loan Default Rate																					12 months
Number of Months the Conditional Default Rate is Calculated Applying Liquidation Rates to Current Period Past Due Balances Excluding Thirty to Fifty Nine Days Past Due																					4 months
Period of decrease in conditional default rate until final rate is achieved (in months)																					28 months																																																																													28 months	28 months	33 months	33 months				18 months
Stress period (in months)																					34 months																																																																													34 months	34 months	42 months	42 months			24 months	24 months
Number of Monthly Delinquency Categories																					5 months
Period of constant conditional default rate (in months)																					1 month																																																																													1 month	1 month					1 month
Loss Recovery Assumption																				2.00%	2.00%	2.00%	2.00%
Conditional Prepayment Rate Base Case Average Number of Months																					3 months
Number of conditional default rate curves modeled in estimating losses																				3
Increased plateau period used to calculate potential change in loss estimate (in months)																																																																																																				4 months	4 months				1 month
Loss Estimate Sensitivity Analysis Increase in Conditional Default Rate Ramp Down Period	5 months
Loss Estimate Sensitivity Analysis Change in Estimate for Increased Conditional Default Rate Plateau Period																																																																																																						$ 2	$ 30
Decreased ramp down period used to calculate potential change in loss estimate (in months)																																																																																																								18 months
Loss Estimate Sensitivity Analysis Change in Estimate for Decreased Conditional Default Rate Ramp Down Period																																																																																																										$ 2	$ 28

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