Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	$ 1,714		$ 1,714			$ 1,344
Accumulated other comprehensive income, net of tax, end of period	1,714		1,714
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	2,384	$ 2,676	2,094	$ 2,719
Other comprehensive income before reclassification, before tax	331	(260)	682	(257)
Reclassification adjustment, before tax	(42)	(59)	(103)	(105)
Effect on other comprehensive income, before tax	289	(319)	579	(362)
Accumulated other comprehensive income, before tax, end of period	2,673	2,357	2,673	2,357
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	822	927	722	942
Other comprehensive income before reclassification, tax	118	(91)	239	(90)
Reclassification adjustment, tax	(15)	(21)	(36)	(37)
Effect on other comprehensive income, tax	103	(112)	203	(127)
Accumulated other comprehensive income, tax, end of period	925	815	925	815
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	1,748	1,542	1,748	1,542	$ 1,562	1,372	$ 1,749	$ 1,777
Other comprehensive income before reclassification, net of tax	213	(169)	443	(167)
Reclassification adjustment, net of tax	(27)	(38)	(67)	(68)
Effect on other comprehensive income, net of tax	186	(207)	376	(235)
Accumulated other comprehensive income, net of tax, end of period	1,748	1,542	1,748	1,542
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	(41)	(35)	(42)	(36)
Other comprehensive income before reclassification, before tax	0	0	0	0
Reclassification adjustment, before tax	1	2	2	3
Effect on other comprehensive income, before tax	1	2	2	3
Accumulated other comprehensive income, before tax, end of period	(40)	(33)	(40)	(33)
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	(13)	(12)	(14)	(12)
Other comprehensive income before reclassification, tax	0	0	0	0
Reclassification adjustment, tax	0	1	1	1
Effect on other comprehensive income, tax	0	1	1	1
Accumulated other comprehensive income, tax, end of period	(13)	(11)	(13)	(11)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	(27)	(22)	(27)	(22)	(28)	(28)	(23)	(24)
Other comprehensive income before reclassification, net of tax	0	0	0	0
Reclassification adjustment, net of tax	1	1	1	2
Effect on other comprehensive income, net of tax	1	1	1	2
Accumulated other comprehensive income, net of tax, end of period	(27)	(22)	(27)	(22)
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	(3)	(14)	1	(12)
Other comprehensive income before reclassification, before tax	(5)	7	(9)	6
Reclassification adjustment, before tax	(2)	(1)	(2)	(2)
Effect on other comprehensive income, before tax	(7)	6	(11)	4
Accumulated other comprehensive income, before tax, end of period	(10)	(8)	(10)	(8)
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	0	(4)	1	(3)
Other comprehensive income before reclassification, tax	(2)	3	(3)	2
Reclassification adjustment, tax	(1)	(1)	(1)	(1)
Effect on other comprehensive income, tax	(3)	2	(4)	1
Accumulated other comprehensive income, tax, end of period	(3)	(2)	(3)	(2)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	(7)	(6)	(7)	(6)	(3)	0	(10)	(9)
Other comprehensive income before reclassification, net of tax	(3)	4	(6)	4
Reclassification adjustment, net of tax	(1)	0	(1)	(1)
Effect on other comprehensive income, net of tax	(4)	4	(7)	3
Accumulated other comprehensive income, net of tax, end of period	(7)	(6)	(7)	(6)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	2,340	2,627	2,053	2,671
Change in unrealized gains, net, on investments available for sale, before tax	289	(319)	579	(362)
Change in pension obligations, before tax	1	2	2	3
Change in life deferred acquisition costs, life policy reserves and other, before tax	(7)	6	(11)	4
Effect on other comprehensive income, before tax	283	(311)	570	(355)
Accumulated other comprehensive income, before tax, end of period	2,623	2,316	2,623	2,316
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	809	911	709	927
Change in unrealized gains, net, on investments available for sale, tax	103	(112)	203	(127)
Change in pension obligations, tax	0	1	1	1
Change in life deferred acquisition costs, life policy reserves and other, tax	(3)	2	(4)	1
Effect on other comprehensive income, tax	100	(109)	200	(125)
Accumulated other comprehensive income, tax, end of period	909	802	909	802
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	1,714	1,514	1,714	1,514	$ 1,531	$ 1,344	$ 1,716	$ 1,744
Change in unrealized gains, net, on investments available for sale, net of tax	186	(207)	376	(235)
Change in pension obligations, net of tax	1	1	1	2
Change in life deferred acquisition costs, life policy reserves and other, net of tax	(4)	4	(7)	3
Effect on other comprehensive income, net of tax	183	(202)	370	(230)
Accumulated other comprehensive income, net of tax, end of period	$ 1,714	$ 1,514	$ 1,714	$ 1,514