Consolidated Variable Interest Entities - Consolidated FG VIE's By Type of Collateral (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Financial guaranty variable interest entities' assets with recourse, at fair value	$ 541	$ 570
Financial guaranty variable interest entities’ liabilities with recourse, at fair value	598	627
Financial guaranty variable interest entities' assets without recourse, at fair value	110	130
Financial guaranty variable interest entities’ liabilities without recourse, at fair value	110	130
Financial guaranty variable interest entities’ assets, at fair value	651	700
Financial guaranty variable interest entities’ liabilities, at fair value	708	757
Manufactured Housing Loans [Member]
Variable Interest Entity [Line Items]
Financial guaranty variable interest entities' assets with recourse, at fair value	61	64
Financial guaranty variable interest entities’ liabilities with recourse, at fair value	62	65
United States [Member] | First Lien [Member] | RMBS [Member]
Variable Interest Entity [Line Items]
Financial guaranty variable interest entities' assets with recourse, at fair value	345	362
Financial guaranty variable interest entities’ liabilities with recourse, at fair value	371	385
United States [Member] | Second Lien [Member] | RMBS [Member]
Variable Interest Entity [Line Items]
Financial guaranty variable interest entities' assets with recourse, at fair value	135	144
Financial guaranty variable interest entities’ liabilities with recourse, at fair value	$ 165	$ 177