Variable Interest Entities - Narrative (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) Entity policies	Dec. 31, 2017 USD ($) Entity policies	Dec. 31, 2016 USD ($) Entity	Dec. 31, 2015 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	$ 14,000,000	$ 30,000,000	$ 38,000,000
Variable Interest Entity, Other Consolidated, Carrying Amount, Assets	87,000,000	86,000,000
Variable Interest Entity, Other Consolidated, Carrying Amount, Liabilities	$ 21,000,000	$ 41,000,000
Variable Interest Entity, Number of Policies Monitored | policies	19,000
Variable Interest Entity, Number of Policies Monitored, Not Within the Scope of ASC 810 | policies	16,000
Variable Interest Entity, Number of Policies that Contain Provisions for Consolidation | policies	110	99
Cumulative Effect of New Accounting Principle in Period of Adoption		$ 32,000,000
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	$ 14,000,000	$ 30,000,000	$ 38,000,000
Number of FG VIE's matured | Entity	0	0	1
Number of VIE that did not require consolidation | Entity	31	32	32	34
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	$ 71,000,000	$ 99,000,000
Difference between the aggregate unpaid principal and aggregate fair value of the VIEs' Assets	350,000,000	361,000,000
Change in the instrument specific credit risk of the VIEs' assets	7,000,000	35,000,000	$ 55,000,000
Unpaid principal for FG VIEs’ liabilities	565,000,000	674,000,000
Unpaid principal for FG VIEs' liabilities with recourse	48,000,000	48,000,000
Unpaid principal for FG VIEs' liabilities without recourse	$ 28,000,000	25,000,000
Net Unrealized Gains (Losses) on FG VIEs’ Liabilities with Recourse due to ISCR [Member]
Credit Risk Derivatives at Fair Value before Effect of Credit Spread Net 1 [Abstract]
Cumulative Effect of New Accounting Principle in Period of Adoption		33,000,000
Net Unrealized Gains (Losses) on FG VIEs’ Liabilities with Recourse due to ISCR [Member] | Accounting Standards Update 2016-01 [Member]
Credit Risk Derivatives at Fair Value before Effect of Credit Spread Net 1 [Abstract]
Cumulative Effect of New Accounting Principle in Period of Adoption		$ 33,000,000