Consolidated Variable Interest Entities - Consolidated FG VIE's By Type of Collateral (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Financial guaranty variable interest entities' assets with recourse, at fair value	$ 570	$ 725
Financial guaranty variable interest entities’ liabilities with recourse, at fair value	627	807
Financial guaranty variable interest entities' assets without recourse, at fair value	130	151
Financial guaranty variable interest entities’ liabilities without recourse, at fair value	130	151
Financial guaranty variable interest entities’ assets, at fair value	700	876
Financial guaranty variable interest entities’ liabilities, at fair value	757	958
Manufactured Housing Loans [Member]
Variable Interest Entity [Line Items]
Financial guaranty variable interest entities' assets with recourse, at fair value	64	74
Financial guaranty variable interest entities’ liabilities with recourse, at fair value	65	75
United States [Member] | First Lien [Member] | Residential Mortgage-Backed Securities (RMBS) [Member]
Variable Interest Entity [Line Items]
Financial guaranty variable interest entities' assets with recourse, at fair value	362	473
Financial guaranty variable interest entities’ liabilities with recourse, at fair value	385	509
United States [Member] | Second Lien [Member] | Residential Mortgage-Backed Securities (RMBS) [Member]
Variable Interest Entity [Line Items]
Financial guaranty variable interest entities' assets with recourse, at fair value	144	178
Financial guaranty variable interest entities’ liabilities with recourse, at fair value	$ 177	$ 223