Variable Interest Entities - Consolidated FG VIE's By Type of Collateral (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Financial guaranty variable interest entities' assets with recourse, at fair value	$ 492	$ 570
Financial guaranty variable interest entities’ liabilities with recourse, at fair value	545	627
Financial guaranty variable interest entities' assets without recourse, at fair value	104	130
Financial guaranty variable interest entities’ liabilities without recourse, at fair value	104	130
Financial guaranty variable interest entities’ assets, at fair value	596	700
Financial guaranty variable interest entities’ liabilities, at fair value	649	757
Manufactured Housing Loans [Member]
Variable Interest Entity [Line Items]
Financial guaranty variable interest entities' assets with recourse, at fair value	55	64
Financial guaranty variable interest entities’ liabilities with recourse, at fair value	57	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	315	362
Financial guaranty variable interest entities’ liabilities with recourse, at fair value	341	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	122	144
Financial guaranty variable interest entities’ liabilities with recourse, at fair value	$ 147	$ 177