Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	$ 210		$ 210	$ 22
Accumulated other comprehensive income, net of tax, end of period	210
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	46	$ 385
Cumulative effect of change in accounting for equity securities, before tax				0	$ (3,155)
Other comprehensive income before reclassification, before tax	244	(217)
Reclassification adjustment, before tax	(2)	(4)
Effect on other comprehensive income, before tax	242	(221)
Accumulated other comprehensive income, before tax, end of period	288	164
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	9	81
Cumulative effect of change in accounting for equity securities, tax				0	(652)
Other comprehensive income before reclassification, tax	51	(45)
Reclassification adjustment, tax	(1)	(1)
Effect on other comprehensive income, tax	50	(46)
Accumulated other comprehensive income, tax, end of period	59	35
Unrealized gains reclassified to retained earnings for ASU 2016-01, after tax				0	(2,503)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	229	129	229	37	304
Other comprehensive income before reclassification, net of tax	193	(172)
Reclassification adjustment, net of tax	(1)	(3)
Effect on other comprehensive income, net of tax	192	(175)
Accumulated other comprehensive income, net of tax, end of period	229	129
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	(16)	(12)
Other comprehensive income before reclassification, before tax	0	0
Reclassification adjustment, before tax	0	0
Effect on other comprehensive income, before tax	0	0
Accumulated other comprehensive income, before tax, end of period	(16)	(12)
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	(2)	(1)
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	(2)	(1)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	(14)	(11)	(14)	(14)	(11)
Other comprehensive income before reclassification, net of tax	0	0
Reclassification adjustment, net of tax	0	0
Effect on other comprehensive income, net of tax	0	0
Accumulated other comprehensive income, net of tax, end of period	(14)	(11)
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)	(10)
Other comprehensive income before reclassification, before tax	0	6
Reclassification adjustment, before tax	(5)	0
Effect on other comprehensive income, before tax	(5)	6
Accumulated other comprehensive income, before tax, end of period	(6)	(4)
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	0	(2)
Other comprehensive income before reclassification, tax	0	1
Reclassification adjustment, tax	(1)	0
Effect on other comprehensive income, tax	(1)	1
Accumulated other comprehensive income, tax, end of period	(1)	(1)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	(5)	(3)	(5)	(1)	(8)
Other comprehensive income before reclassification, net of tax	0	5
Reclassification adjustment, net of tax	(4)	0
Effect on other comprehensive income, net of tax	(4)	5
Accumulated other comprehensive income, net of tax, end of period	(5)	(3)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	29	363
Cumulative effect of change in accounting for equity securities, before tax				0	(3,155)
Change in unrealized gains, net, on investments available for sale, before tax	242	(221)
Change in pension obligations, before tax	0	0
Change in life deferred acquisition costs, life policy reserves and other, before tax	(5)	6
Effect on other comprehensive income, before tax	237	(215)
Accumulated other comprehensive income, before tax, end of period	266	148
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	7	78
Cumulative effect of change in accounting for equity securities, tax				0	(652)
Change in unrealized gains, net, on investments available for sale, tax	50	(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	49	(45)
Accumulated other comprehensive income, tax, end of period	56	33
Unrealized gains reclassified to retained earnings for ASU 2016-01, after tax			0	0	(2,503)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	210	115	$ 210	22	285
Cumulative effect of change in accounting for equity securities, net					(2,503)
Change in unrealized gains, net, on investments available for sale, net of tax	192	(175)
Change in pension obligations, net of tax	0	0
Change in life deferred acquisition costs, life policy reserves and other, net of tax	(4)	5
Effect on other comprehensive income, net of tax	188	(170)
Accumulated other comprehensive income, net of tax, end of period	210	115
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	46	3,540
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	9	733
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period				37	2,807
Previously Reported | Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	29	3,518
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	$ 7	$ 730
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period				$ 22	$ 2,788