Expected Loss to be Paid - Net Expected Loss to be Paid (Recovered) and Net Economic Loss Development (Benefit) by Accounting Model (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid (recovered) after recoveries for R&W		$ 1,198	[1]	$ 1,391	[1]	$ 1,169
Total economic loss development (benefit)		139		319
Public Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid (recovered) after recoveries for R&W		904	[1]	809	[1]	348
Total economic loss development (benefit)		269		405
Structured Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid (recovered) after recoveries for R&W		294	[1]	582	[1]	$ 821
Total economic loss development (benefit)		(130)		(86)
Financial Guarantee Accounted for as Insurance Contracts [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid (recovered) after recoveries for R&W		1,083		1,239
Total economic loss development (benefit)		164		385
Financial Guarantee Accounted for as Insurance Contracts [Member] | Public Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid (recovered) after recoveries for R&W		904		809
Total economic loss development (benefit)		269		410
Financial Guarantee Accounted for as Insurance Contracts [Member] | Structured Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid (recovered) after recoveries for R&W		179		430
Total economic loss development (benefit)		(105)		(25)
Financial Guarantee Variable Interest Entities And Other [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid (recovered) after recoveries for R&W	[2]	105		136
Total economic loss development (benefit)	[3]	(8)		16
Financial Guarantee Variable Interest Entities And Other [Member] | Public Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid (recovered) after recoveries for R&W	[2]	0		0
Total economic loss development (benefit)	[3]	0		0
Financial Guarantee Variable Interest Entities And Other [Member] | Structured Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid (recovered) after recoveries for R&W	[2]	105		136
Total economic loss development (benefit)	[3]	(8)		16
Financial Guarantee Accounted for as Credit Derivatives [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid (recovered) after recoveries for R&W	[4]	10		16
Total economic loss development (benefit)	[5]	(17)		(82)
Financial Guarantee Accounted for as Credit Derivatives [Member] | Public Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid (recovered) after recoveries for R&W	[4]	0		0
Total economic loss development (benefit)	[5]	0		(5)
Financial Guarantee Accounted for as Credit Derivatives [Member] | Structured Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid (recovered) after recoveries for R&W	[4]	10		16
Total economic loss development (benefit)	[5]	$ (17)		$ (77)

[1] Includes expected LAE to be paid of $12 million as of December 31, 2016 and $12 million as of December 31, 2015.

[2] Refer to Note 9, Consolidated Variable Interest Entities.

[3] Refer to Note 9, Consolidated Variable Interest Entities.

[4] Refer to Note 8, Contracts Accounted for as Credit Derivatives.

[5] Refer to Note 8, Contracts Accounted for as Credit Derivatives.