Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 161	$ 208	$ 433	$ 678
Unrealized holding gains (losses) arising during the period on:
Investments with no other-than-temporary impairment, net of tax provision (benefit) of $(11), $10, $(42) and $63	(59)	27	(245)	133
Investments with other-than-temporary impairment, net of tax provision (benefit) of $(3), $(7), $(5) and $44	(16)	(15)	(21)	81
Unrealized holding gains (losses) arising during the period, net of tax	(75)	12	(266)	214
Less: reclassification adjustment for gains (losses) included in net income (loss), net of tax provision (benefit) of $0, $3, $(2) and $29	(7)	4	(11)	52
Change in net unrealized gains (losses) on investments	(68)	8	(255)	162
Net unrealized gains (losses) arising during the period on financial guaranty variable interest entities' liabilities with recourse attributable to changes in instrument-specific credit risk, net of tax provision (benefit) of $(1), $-, $(1) and $- (see Note 1)	(5)	0	(6)	0
Less: reclassification adjustment for gains (losses) included in net income (loss), net of tax provision (benefit) of $0, $-, $(1) and $-	(2)	0	(5)	0
Change in net unrealized gains (losses) on financial guaranty variable interest entities' liabilities with recourse	(3)	0	(1)	0
Other, net of tax provision	(3)	3	(6)	15
Other comprehensive income (loss)	(74)	11	(262)	177
Comprehensive income (loss)	$ 87	$ 219	$ 171	$ 855