Expected Loss to be Paid - Net Expected Loss to be Paid After Net Expected Recoveries for Breaches of R&W Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Schedule of Expected Losses to be Paid [Line Items]
Guarantor Obligations, Net Expected Loss To Be Paid After Recoveries For Representations And Warranties On Business Combinations			$ 21
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	$ 1,244	$ 1,337	1,198	$ 1,391
Economic Loss Development / (Benefit)	47	22	94	81
Accretion of discount	8	6	16	15
Changes in discount rates	23	45	34	108
Changes in timing and assumptions	16	(29)	44	(42)
(Paid) Recovered Losses	6	(33)	(16)	(146)
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	1,297	1,326	$ 1,297	1,326
Period after the end of the reporting period within which the ceded paid losses are typically settled (in days)			45 days
Loss and LAE Reserve paid	7	7	$ 9	9
Expected LAE to be paid	18		18		$ 12
Public Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Guarantor Obligations, Net Expected Loss To Be Paid After Recoveries For Representations And Warranties On Business Combinations			13
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	1,011	903	904	809
Economic Loss Development / (Benefit)	79	109	198	208
(Paid) Recovered Losses	(4)	(12)	(29)	(17)
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	1,086	1,000	1,086	1,000
Public Finance [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Guarantor Obligations, Net Expected Loss To Be Paid After Recoveries For Representations And Warranties On Business Combinations			0
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	970	864	871	771
Economic Loss Development / (Benefit)	78	111	202	209
(Paid) Recovered Losses	(4)	(12)	(29)	(17)
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	1,044	963	1,044	963
Public Finance [Member] | Non United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Guarantor Obligations, Net Expected Loss To Be Paid After Recoveries For Representations And Warranties On Business Combinations			13
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	41	39	33	38
Economic Loss Development / (Benefit)	1	(2)	(4)	(1)
(Paid) Recovered Losses	0	0	0	0
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	42	37	42	37
RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Guarantor Obligations, Net Expected Loss To Be Paid After Recoveries For Representations And Warranties On Business Combinations			0
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	197	293	206	409
Economic Loss Development / (Benefit)	(29)	(81)	(51)	(112)
(Paid) Recovered Losses	14	(20)	27	(105)
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	182	192	182	192
Triple-X Life Insurance Transaction [Member]
Schedule of Expected Losses to be Paid [Line Items]
Guarantor Obligations, Net Expected Loss To Be Paid After Recoveries For Representations And Warranties On Business Combinations			0
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	1	102	54	99
Economic Loss Development / (Benefit)	(2)	(2)	(55)	2
(Paid) Recovered Losses	(3)	0	(3)	(1)
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	(4)	100	(4)	100
Student Loan [Member]
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Economic Loss Development / (Benefit)	1		1
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	33		33
Other structured finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Guarantor Obligations, Net Expected Loss To Be Paid After Recoveries For Representations And Warranties On Business Combinations			8
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	35	39	34	74
Economic Loss Development / (Benefit)	(1)	(4)	2	(17)
(Paid) Recovered Losses	(1)	(1)	(11)	(23)
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	33	34	33	34
Structured Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Guarantor Obligations, Net Expected Loss To Be Paid After Recoveries For Representations And Warranties On Business Combinations			8
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Beginning of Period, Net Expected Loss to be Paid After Recoveries for R&W	233	434	294	582
Economic Loss Development / (Benefit)	(32)	(87)	(104)	(127)
(Paid) Recovered Losses	10	(21)	13	(129)
End of Period, Net Expected Loss to be Paid After Recoveries for R&W	211	326	211	326
MBIA UK Insurance Limited [Member]
Schedule of Expected Losses to be Paid [Line Items]
Guarantor Obligations, Net Expected Loss To Be Paid After Recoveries For Representations And Warranties On Business Combinations	$ 0	$ 0	$ 21	$ 0