Expected Losses to be Paid (Details 8) (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2013 risk		Sep. 30, 2012	Sep. 30, 2013 risk		Sep. 30, 2012	Dec. 31, 2012 risk
Guarantor Obligations [Line Items]
Number of Risks as of the end of the period with R&W Benefit Recorded (in policies)	50	[1]		50	[1]		53	[1]
Outstanding Principal and Interest on Representations and Warranties Policies	$ 5,931			$ 5,931			$ 7,198
Inclusion of new deals with breaches of R&W during period	0		0	6		(5)
Change in recovery assumptions as the result of additional file review and recovery success	69		0	86		70
Estimated increase (decrease) in defaults that will result in additional breaches	13		10	10		(14)
Results of settlements	0		0	180		48
Accretion of discount on balance	4		2	12		10
Expected Future Recoveries for Breached Representations and Warranties Development and Accretion of Discount	86		12	294		109
Minimum
Guarantor Obligations [Line Items]
Estimated Period of Recoveries on Transactions Backed by Heloc and Closed End Second Lien Loans Not Subject to settlement Agreements	2 years
Maximum
Guarantor Obligations [Line Items]
Estimated Period of Recoveries on Transactions Backed by Heloc and Closed End Second Lien Loans Not Subject to settlement Agreements	4 years
Prime first lien
Guarantor Obligations [Line Items]
Number of Risks as of the end of the period with R&W Benefit Recorded (in policies)	1	[1]		1	[1]		1	[1]
Outstanding Principal and Interest on Representations and Warranties Policies	38			38			44
Expected Future Recoveries for Breached Representations and Warranties Development and Accretion of Discount	(1)		0	(1)		1
Alt-A first lien
Guarantor Obligations [Line Items]
Number of Risks as of the end of the period with R&W Benefit Recorded (in policies)	25	[1]		25	[1]		26	[1]
Outstanding Principal and Interest on Representations and Warranties Policies	3,607			3,607			4,173
Expected Future Recoveries for Breached Representations and Warranties Development and Accretion of Discount	37		0	24		44
Option ARM
Guarantor Obligations [Line Items]
Number of Risks as of the end of the period with R&W Benefit Recorded (in policies)	9	[1]		9	[1]		10	[1]
Outstanding Principal and Interest on Representations and Warranties Policies	695			695			1,183
Expected Future Recoveries for Breached Representations and Warranties Development and Accretion of Discount	40		(7)	206		55
First mortgage, subprime
Guarantor Obligations [Line Items]
Number of Risks as of the end of the period with R&W Benefit Recorded (in policies)	5	[1]		5	[1]		5	[1]
Outstanding Principal and Interest on Representations and Warranties Policies	991			991			989
Expected Future Recoveries for Breached Representations and Warranties Development and Accretion of Discount	7		11	6		3
Closed end second lien and HELOCs
Guarantor Obligations [Line Items]
Number of Risks as of the end of the period with R&W Benefit Recorded (in policies)	4	[1]		4	[1]		4	[1]
Outstanding Principal and Interest on Representations and Warranties Policies	164			164			260
Expected Future Recoveries for Breached Representations and Warranties Development and Accretion of Discount	1		2	(11)		0
HELOCs
Guarantor Obligations [Line Items]
Number of Risks as of the end of the period with R&W Benefit Recorded (in policies)	6	[1]		6	[1]		7	[1]
Outstanding Principal and Interest on Representations and Warranties Policies	436			436			549
Expected Future Recoveries for Breached Representations and Warranties Development and Accretion of Discount	$ 2		$ 6	$ 70		$ 6

[1] A risk represents the aggregate of the financial guaranty policies that share the same revenue source for purposes of making Debt Service payments. This table shows the full future Debt Service (not just the amount of Debt Service expected to be reimbursed) for risks with projected future R&W benefit, whether pursuant to an agreement or not.