Consolidated Variable Interest Entities - Consolidated FG VIE's By Type of Collateral (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Financial guaranty variable interest entities' assets with recourse, at fair value	$ 519	$ 570
Financial guaranty variable interest entities’ liabilities with recourse, at fair value	571	627
Financial guaranty variable interest entities' assets without recourse, at fair value	108	130
Financial guaranty variable interest entities’ liabilities without recourse, at fair value	108	130
Financial guaranty variable interest entities’ assets, at fair value	627	700
Financial guaranty variable interest entities’ liabilities, at fair value	679	757
Manufactured Housing Loans [Member]
Variable Interest Entity [Line Items]
Financial guaranty variable interest entities' assets with recourse, at fair value	58	64
Financial guaranty variable interest entities’ liabilities with recourse, at fair value	60	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	332	362
Financial guaranty variable interest entities’ liabilities with recourse, at fair value	356	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	129	144
Financial guaranty variable interest entities’ liabilities with recourse, at fair value	$ 155	$ 177