Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	$ 1,531		$ 1,344
Accumulated other comprehensive income, net of tax, end of period	1,531
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	2,094	$ 2,719
Other comprehensive income before reclassification, before tax	351	3
Reclassification adjustment, before tax	(61)	(46)
Effect on other comprehensive income, before tax	290	(43)
Accumulated other comprehensive income, before tax, end of period	2,384	2,676
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	722	942
Other comprehensive income before reclassification, tax	121	1
Reclassification adjustment, tax	(21)	(16)
Effect on other comprehensive income, tax	100	(15)
Accumulated other comprehensive income, tax, end of period	822	927
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	1,562	1,749	1,372	$ 1,777
Other comprehensive income before reclassification, net of tax	230	2
Reclassification adjustment, net of tax	(40)	(30)
Effect on other comprehensive income, net of tax	190	(28)
Accumulated other comprehensive income, net of tax, end of period	1,562	1,749
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	(42)	(36)
Other comprehensive income before reclassification, before tax	0	0
Reclassification adjustment, before tax	1	1
Effect on other comprehensive income, before tax	1	1
Accumulated other comprehensive income, before tax, end of period	(41)	(35)
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	(14)	(12)
Other comprehensive income before reclassification, tax	0	0
Reclassification adjustment, tax	1	0
Effect on other comprehensive income, tax	1	0
Accumulated other comprehensive income, tax, end of period	(13)	(12)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	(28)	(23)	(28)	(24)
Other comprehensive income before reclassification, net of tax	0	0
Reclassification adjustment, net of tax	0	1
Effect on other comprehensive income, net of tax	0	1
Accumulated other comprehensive income, net of tax, end of period	(28)	(23)
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	1	(12)
Other comprehensive income before reclassification, before tax	(4)	(1)
Reclassification adjustment, before tax	0	(1)
Effect on other comprehensive income, before tax	(4)	(2)
Accumulated other comprehensive income, before tax, end of period	(3)	(14)
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	1	(3)
Other comprehensive income before reclassification, tax	(1)	(1)
Reclassification adjustment, tax	0	0
Effect on other comprehensive income, tax	(1)	(1)
Accumulated other comprehensive income, tax, end of period	0	(4)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	(3)	(10)	0	(9)
Other comprehensive income before reclassification, net of tax	(3)	0
Reclassification adjustment, net of tax	0	(1)
Effect on other comprehensive income, net of tax	(3)	(1)
Accumulated other comprehensive income, net of tax, end of period	(3)	(10)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	2,053	2,671
Change in unrealized gains, net, on investments available for sale, before tax	290	(43)
Change in pension obligations, before tax	1	1
Change in life deferred acquisition costs, life policy reserves and other, before tax	(4)	(2)
Effect on other comprehensive income, before tax	287	(44)
Accumulated other comprehensive income, before tax, end of period	2,340	2,627
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	709	927
Change in unrealized gains, net, on investments available for sale, tax	100	(15)
Change in pension obligations, tax	1	0
Change in life deferred acquisition costs, life policy reserves and other, tax	(1)	(1)
Effect on other comprehensive income, tax	100	(16)
Accumulated other comprehensive income, tax, end of period	809	911
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	1,531	1,716	$ 1,344	$ 1,744
Change in unrealized gains, net, on investments available for sale, net of tax	190	(28)
Change in pension obligations, net of tax	0	1
Change in life deferred acquisition costs, life policy reserves and other, net of tax	(3)	(1)
Effect on other comprehensive income, net of tax	187	(28)
Accumulated other comprehensive income, net of tax, end of period	$ 1,531	$ 1,716