Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	$ 2,047		$ 2,047			$ 1,693
Accumulated other comprehensive income, net of tax, end of period	2,047		2,047
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	2,977	$ 2,673	2,625	$ 2,094
Other comprehensive income before reclassification, before tax	193	119	694	801
Reclassification adjustment, before tax	(4)	(57)	153	(160)
Effect on other comprehensive income, before tax	189	62	541	641
Accumulated other comprehensive income, before tax, end of period	3,166	2,735	3,166	2,735
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	1,031	925	908	722
Other comprehensive income before reclassification, tax	67	41	243	280
Reclassification adjustment, tax	(1)	(20)	(54)	(56)
Effect on other comprehensive income, tax	66	21	189	224
Accumulated other comprehensive income, tax, end of period	1,097	946	1,097	946
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	2,069	1,789	2,069	1,789	$ 1,946	1,717	$ 1,748	$ 1,372
Other comprehensive income before reclassification, net of tax	126	78	451	521
Reclassification adjustment, net of tax	(3)	(37)	(99)	(104)
Effect on other comprehensive income, net of tax	123	41	352	417
Accumulated other comprehensive income, net of tax, end of period	2,069	1,789	2,069	1,789
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	(25)	(40)	(26)	(42)
Other comprehensive income before reclassification, before tax	0	0	0	0
Reclassification adjustment, before tax	1	0	2	2
Effect on other comprehensive income, before tax	1	0	2	2
Accumulated other comprehensive income, before tax, end of period	(24)	(40)	(24)	(40)
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	(8)	(13)	(8)	(14)
Other comprehensive income before reclassification, tax	0	0	0	0
Reclassification adjustment, tax	1	0	1	1
Effect on other comprehensive income, tax	1	0	1	1
Accumulated other comprehensive income, tax, end of period	(7)	(13)	(7)	(13)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	(17)	(27)	(17)	(27)	(17)	(18)	(27)	(28)
Other comprehensive income before reclassification, net of tax	0	0	0	0
Reclassification adjustment, net of tax	0	0	1	1
Effect on other comprehensive income, net of tax	0	0	1	1
Accumulated other comprehensive income, net of tax, end of period	(17)	(27)	(17)	(27)
Accumulated Net Unrealized Gain (Loss) on Deferred Costs, Reserves And Other
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	(6)	(10)	(9)	1
Other comprehensive income before reclassification, before tax	1	(4)	4	(13)
Reclassification adjustment, before tax	(3)	1	(3)	(1)
Effect on other comprehensive income, before tax	(2)	(3)	1	(14)
Accumulated other comprehensive income, before tax, end of period	(8)	(13)	(8)	(13)
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	(2)	(3)	(3)	1
Other comprehensive income before reclassification, tax	0	(1)	1	(4)
Reclassification adjustment, tax	(1)	1	(1)	0
Effect on other comprehensive income, tax	(1)	0	0	(4)
Accumulated other comprehensive income, tax, end of period	(3)	(3)	(3)	(3)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	(5)	(10)	(5)	(10)	(4)	(6)	(7)	0
Other comprehensive income before reclassification, net of tax	1	(3)	3	(9)
Reclassification adjustment, net of tax	(2)	0	(2)	(1)
Effect on other comprehensive income, net of tax	(1)	(3)	1	(10)
Accumulated other comprehensive income, net of tax, end of period	(5)	(10)	(5)	(10)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	2,946	2,623	2,590	2,053
Change in unrealized gains, net, on investments available for sale, before tax	189	62	541	641
Change in pension obligations, before tax	1	0	2	2
Change in life deferred acquisition costs, life policy reserves and other, before tax	(2)	(3)	1	(14)
Effect on other comprehensive income, before tax	188	59	544	629
Accumulated other comprehensive income, before tax, end of period	3,134	2,682	3,134	2,682
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	1,021	909	897	709
Change in unrealized gains, net, on investments available for sale, tax	66	21	189	224
Change in pension obligations, tax	1	0	1	1
Change in life deferred acquisition costs, life policy reserves and other, tax	(1)	0	0	(4)
Effect on other comprehensive income, tax	66	21	190	221
Accumulated other comprehensive income, tax, end of period	1,087	930	1,087	930
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	2,047	1,752	2,047	1,752	$ 1,925	$ 1,693	$ 1,714	$ 1,344
Change in unrealized gains, net, on investments available for sale, net of tax	123	41	352	417
Change in pension obligations, net of tax	0	0	1	1
Change in life deferred acquisition costs, life policy reserves and other, net of tax	(1)	(3)	1	(10)
Effect on other comprehensive income, net of tax	122	38	354	408
Accumulated other comprehensive income, net of tax, end of period	$ 2,047	$ 1,752	$ 2,047	$ 1,752