Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	$ 1,925		$ 1,925			$ 1,693
Accumulated other comprehensive income, net of tax, end of period	1,925		1,925
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	2,756	$ 2,384	2,625	$ 2,094
Other comprehensive income before reclassification, before tax	211	331	501	682
Reclassification adjustment, before tax	10	(42)	(149)	(103)
Effect on other comprehensive income, before tax	221	289	352	579
Accumulated other comprehensive income, before tax, end of period	2,977	2,673	2,977	2,673
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	954	822	908	722
Other comprehensive income before reclassification, tax	74	118	176	239
Reclassification adjustment, tax	3	(15)	(53)	(36)
Effect on other comprehensive income, tax	77	103	123	203
Accumulated other comprehensive income, tax, end of period	1,031	925	1,031	925
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	1,946	1,748	1,946	1,748	$ 1,802	1,717	$ 1,562	$ 1,372
Other comprehensive income before reclassification, net of tax	137	213	325	443
Reclassification adjustment, net of tax	7	(27)	(96)	(67)
Effect on other comprehensive income, net of tax	144	186	229	376
Accumulated other comprehensive income, net of tax, end of period	1,946	1,748	1,946	1,748
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	(25)	(41)	(26)	(42)
Other comprehensive income before reclassification, before tax	0	0	0	0
Reclassification adjustment, before tax	0	1	1	2
Effect on other comprehensive income, before tax	0	1	1	2
Accumulated other comprehensive income, before tax, end of period	(25)	(40)	(25)	(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	0	0	0	1
Effect on other comprehensive income, tax	0	0	0	1
Accumulated other comprehensive income, tax, end of period	(8)	(13)	(8)	(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)	(28)	(28)
Other comprehensive income before reclassification, net of tax	0	0	0	0
Reclassification adjustment, net of tax	0	1	1	1
Effect on other comprehensive income, net of tax	0	1	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	(7)	(3)	(9)	1
Other comprehensive income before reclassification, before tax	0	(5)	3	(9)
Reclassification adjustment, before tax	1	(2)	0	(2)
Effect on other comprehensive income, before tax	1	(7)	3	(11)
Accumulated other comprehensive income, before tax, end of period	(6)	(10)	(6)	(10)
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	(2)	0	(3)	1
Other comprehensive income before reclassification, tax	(1)	(2)	1	(3)
Reclassification adjustment, tax	1	(1)	0	(1)
Effect on other comprehensive income, tax	0	(3)	1	(4)
Accumulated other comprehensive income, tax, end of period	(2)	(3)	(2)	(3)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	(4)	(7)	(4)	(7)	(5)	(6)	(3)	0
Other comprehensive income before reclassification, net of tax	1	(3)	2	(6)
Reclassification adjustment, net of tax	0	(1)	0	(1)
Effect on other comprehensive income, net of tax	1	(4)	2	(7)
Accumulated other comprehensive income, net of tax, end of period	(4)	(7)	(4)	(7)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	2,724	2,340	2,590	2,053
Change in unrealized gains, net, on investments available for sale, before tax	221	289	352	579
Change in pension obligations, before tax	0	1	1	2
Change in life deferred acquisition costs, life policy reserves and other, before tax	1	(7)	3	(11)
Effect on other comprehensive income, before tax	222	283	356	570
Accumulated other comprehensive income, before tax, end of period	2,946	2,623	2,946	2,623
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	944	809	897	709
Change in unrealized gains, net, on investments available for sale, tax	77	103	123	203
Change in pension obligations, tax	0	0	0	1
Change in life deferred acquisition costs, life policy reserves and other, tax	0	(3)	1	(4)
Effect on other comprehensive income, tax	77	100	124	200
Accumulated other comprehensive income, tax, end of period	1,021	909	1,021	909
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	1,925	1,714	1,925	1,714	$ 1,780	$ 1,693	$ 1,531	$ 1,344
Change in unrealized gains, net, on investments available for sale, net of tax	144	186	229	376
Change in pension obligations, net of tax	0	1	1	1
Change in life deferred acquisition costs, life policy reserves and other, net of tax	1	(4)	2	(7)
Effect on other comprehensive income, net of tax	145	183	232	370
Accumulated other comprehensive income, net of tax, end of period	$ 1,925	$ 1,714	$ 1,925	$ 1,714