Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Unrealized gains reclassified to retained earnings for ASU 2016-01, after tax			$ 2,503		$ 0
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	$ 115		115	$ 2,788
Accumulated other comprehensive income, net of tax, end of period	115
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	385	$ 2,625
Cumulative effect of change in accounting for equity securities, before tax				(3,155)		$ 0
Other comprehensive income before reclassification, before tax	(217)	290
Reclassification adjustment, before tax	(4)	(159)
Effect on other comprehensive income, before tax	(221)	131
Accumulated other comprehensive income, before tax, end of period	164	2,756
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	81	908
Cumulative effect of change in accounting for equity securities, tax				(652)		0
Other comprehensive income before reclassification, tax	(45)	102
Reclassification adjustment, tax	(1)	(56)
Effect on other comprehensive income, tax	(46)	46
Accumulated other comprehensive income, tax, end of period	35	954
Unrealized gains reclassified to retained earnings for ASU 2016-01, after tax				(2,503)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	129	1,802	129	304	1,802	1,717
Cumulative effect of change in accounting for equity securities, net						0
Other comprehensive income before reclassification, net of tax	(172)	188
Reclassification adjustment, net of tax	(3)	(103)
Effect on other comprehensive income, net of tax	(175)	85
Accumulated other comprehensive income, net of tax, end of period	129	1,802
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	(12)	(26)
Other comprehensive income before reclassification, before tax	0	0
Reclassification adjustment, before tax	0	1
Effect on other comprehensive income, before tax	0	1
Accumulated other comprehensive income, before tax, end of period	(12)	(25)
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	(1)	(8)
Other comprehensive income before reclassification, tax	0	0
Reclassification adjustment, tax	0	0
Effect on other comprehensive income, tax	0	0
Accumulated other comprehensive income, tax, end of period	(1)	(8)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	(11)	(17)	(11)	(11)	(17)	(18)
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	(11)	(17)
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	(10)	(9)
Other comprehensive income before reclassification, before tax	6	3
Reclassification adjustment, before tax	0	(1)
Effect on other comprehensive income, before tax	6	2
Accumulated other comprehensive income, before tax, end of period	(4)	(7)
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	(2)	(3)
Other comprehensive income before reclassification, tax	1	2
Reclassification adjustment, tax	0	(1)
Effect on other comprehensive income, tax	1	1
Accumulated other comprehensive income, tax, end of period	(1)	(2)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	(3)	(5)	(3)	(8)	(5)	(6)
Other comprehensive income before reclassification, net of tax	5	1
Reclassification adjustment, net of tax	0	0
Effect on other comprehensive income, net of tax	5	1
Accumulated other comprehensive income, net of tax, end of period	(3)	(5)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	363	2,590
Cumulative effect of change in accounting for equity securities, before tax				(3,155)		0
Change in unrealized gains, net, on investments available for sale, before tax	(221)	131
Change in pension obligations, before tax	0	1
Change in life deferred acquisition costs, life policy reserves and other, before tax	6	2
Effect on other comprehensive income, before tax	(215)	134
Accumulated other comprehensive income, before tax, end of period	148	2,724
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	78	897
Cumulative effect of change in accounting for equity securities, tax				(652)		0
Change in unrealized gains, net, on investments available for sale, tax	(46)	46
Change in pension obligations, tax	0	0
Change in life deferred acquisition costs, life policy reserves and other, tax	1	1
Effect on other comprehensive income, tax	(45)	47
Accumulated other comprehensive income, tax, end of period	33	944
Unrealized gains reclassified to retained earnings for ASU 2016-01, after tax			(2,503)	(2,503)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	115	1,780	$ 115	285	$ 1,780	1,693
Cumulative effect of change in accounting for equity securities, net						0
Change in unrealized gains, net, on investments available for sale, net of tax	(175)	85
Change in pension obligations, net of tax	0	1
Change in life deferred acquisition costs, life policy reserves and other, net of tax	5	1
Effect on other comprehensive income, net of tax	(170)	87
Accumulated other comprehensive income, net of tax, end of period	115	1,780
Previously Reported | Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	3,540	2,625
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	733	908
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period				2,807		1,717
Previously Reported | Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	3,518	2,590
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	$ 730	$ 897
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period				$ 2,788		$ 1,693