Consolidated Variable Interest Entities - Narrative (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) Entity	Dec. 31, 2016 USD ($) Entity	Dec. 31, 2015 USD ($) Entity	Dec. 31, 2014 Entity
Variable Interest Entity [Line Items]
Net fair value gains and losses on FG VIEs are expected to reverse to zero at maturity of the VIE debt	$ 0
Trustee report general preparation period	30 days
Credit Risk Derivatives at Fair Value before Effect of Credit Spread Net 1 [Abstract]
Fair value gains (losses) on financial guaranty variable interest entities	$ 30,000,000	$ 38,000,000	$ 38,000,000
Variable Interest Entity, Primary Beneficiary [Member]
Credit Risk Derivatives at Fair Value before Effect of Credit Spread Net 1 [Abstract]
Fair value gains (losses) on financial guaranty variable interest entities	$ 30,000,000	$ 38,000,000	$ 38,000,000
Number of FG VIE's matured | Entity	0	1	2
Number of VIE that did not require consolidation | Entity	32	32	34	32
Variable Interest Entity, Not Primary Beneficiary, Aggregated Disclosure [Member]
Credit Risk Derivatives at Fair Value before Effect of Credit Spread Net 1 [Abstract]
Number of VIE that did not require consolidation | Entity	510	600
Residential Mortgage Backed Securities and Other Insurance Products [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Credit Risk Derivatives at Fair Value before Effect of Credit Spread Net 1 [Abstract]
Total unpaid principal balance for the VIEs' assets that were over 90 days or more past due	$ 99,000,000	$ 137,000,000
Difference between the aggregate unpaid principal and aggregate fair value of the VIEs' Assets	361,000,000	432,000,000
Change in the instrument specific credit risk of the VIEs' assets	35,000,000	55,000,000	$ 90,000,000
Unpaid principal for FG VIEs’ liabilities with recourse	674,000,000	871,000,000
Unpaid principal for FG VIEs' liabilities with and without recourse	$ 73,000,000	$ 109,000,000