Consolidated Variable Interest Entities - Effect of Consolidating FG VIE's on Financial Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Net earned premiums	$ 178	$ 186	$ 162	$ 164	$ 236	$ 231	$ 214	$ 183	$ 690	$ 864	$ 766
Net investment income	96	99	101	122	117	94	98	99	418	408	423
Net realized investment gains (losses)	(14)	7	15	32	(24)	(2)	10	(13)	40	(29)	(26)
Fair value gains (losses) on financial guaranty variable interest entities									30	38	38
Loss and LAE	(34)	(223)	(72)	(59)	(112)	9	(102)	(90)	(388)	(295)	(424)
Income (loss) before income taxes	156	313	150	372	271	480	201	65	991	1,017	1,431
Provision (benefit) for income taxes	104	105	(3)	55	74	1	55	6	261	136	375
Net income (loss)	$ 52	$ 208	$ 153	$ 317	$ 197	$ 479	$ 146	$ 59	730	881	1,056
Net cash flows provided by (used in) operating activities									433	(132)	(71)
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Net earned premiums									(15)	(16)	(21)
Net investment income									(5)	(10)	(32)
Net realized investment gains (losses)									0	1	10
Fair value gains (losses) on financial guaranty variable interest entities									30	38	38
Bargain purchase gain									0	0	2
Loss and LAE									7	7	28
Income (loss) before income taxes									17	20	25
Provision (benefit) for income taxes									6	7	8
Net income (loss)									11	13	17
Net cash flows provided by (used in) operating activities									19	24	$ 43
Effect on shareholders’ equity (decrease) increase									$ 2	$ (9)