Contracts Accounted for as Insurance - Net Earned Premiums (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Financial Guarantee Insurance Premiums [Line Items]
Scheduled net earned premiums									$ 381		$ 416		$ 415
Accelerations
Refundings									390		294		133
Terminations									79		37		3
Total Accelerations									469		331		136
Accretion of discount on net premiums receivable									14		17		16
Financial guaranty insurance net earned premiums									864		764		567
Other									0		2		3
Net	$ 236	$ 231	$ 214	$ 183	$ 192	$ 213	$ 219	$ 142	864	[1]	766	[1]	570	[1]
Variable Interest Entity, Primary Beneficiary [Member]
Accelerations
Net									$ 16		$ 21		$ 32

[1] Excludes $16 million, $21 million and $32 million for the year ended December 31, 2016, 2015 and 2014, respectively, related to consolidated FG VIEs.