Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 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	$ (4)		$ (4)		(4)		$ 2,788
Accumulated other comprehensive income, net of tax, end of period	(4)		(4)
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	84	$ 2,977	385	$ 2,625
Cumulative effect of change in accounting for equity securities, before tax							(3,155)			$ 0
Other comprehensive income before reclassification, before tax	(76)	193	(371)	694
Reclassification adjustment, before tax	(1)	(4)	7	(153)
Effect on other comprehensive income, before tax	(77)	189	(378)	541
Accumulated other comprehensive income, before tax, end of period	7	3,166	7	3,166
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	17	1,031	81	908
Cumulative effect of change in accounting for equity securities, tax							(652)			0
Other comprehensive income before reclassification, tax	(17)	67	(80)	243
Reclassification adjustment, tax	0	(1)	(1)	(54)
Effect on other comprehensive income, tax	(17)	66	(81)	189
Accumulated other comprehensive income, tax, end of period	0	1,097	0	1,097
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	7	2,069	7	2,069	7	$ 67	304	2,069	$ 1,946	1,717
Other comprehensive income before reclassification, net of tax	(59)	126	(291)	451
Reclassification adjustment, net of tax	(1)	(3)	(6)	(99)
Effect on other comprehensive income, net of tax	(60)	123	(297)	352
Accumulated other comprehensive income, net of tax, end of period	7	2,069	7	2,069
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	(11)	(25)	(12)	(26)
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	(11)	(24)	(11)	(24)
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	(1)	(8)	(1)	(8)
Other comprehensive income before reclassification, tax	0	0	0	0
Reclassification adjustment, tax	0	1	0	1
Effect on other comprehensive income, tax	0	1	0	1
Accumulated other comprehensive income, tax, end of period	(1)	(7)	(1)	(7)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	(10)	(17)	(10)	(17)	(10)	(10)	(11)	(17)	(17)	(18)
Other comprehensive income before reclassification, net of tax	0	0	0	0
Reclassification adjustment, net of tax	0	0	1	1
Effect on other comprehensive income, net of tax	0	0	1	1
Accumulated other comprehensive income, net of tax, end of period	(10)	(17)	(10)	(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	(2)	(6)	(10)	(9)
Other comprehensive income before reclassification, before tax	0	1	6	4
Reclassification adjustment, before tax	1	(3)	3	(3)
Effect on other comprehensive income, before tax	1	(2)	9	1
Accumulated other comprehensive income, before tax, end of period	(1)	(8)	(1)	(8)
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	0	(2)	(2)	(3)
Other comprehensive income before reclassification, tax	0	0	1	1
Reclassification adjustment, tax	0	(1)	1	(1)
Effect on other comprehensive income, tax	0	(1)	2	0
Accumulated other comprehensive income, tax, end of period	0	(3)	0	(3)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	(1)	(5)	(1)	(5)	(1)	(2)	(8)	(5)	(4)	(6)
Other comprehensive income before reclassification, net of tax	0	1	5	3
Reclassification adjustment, net of tax	1	(2)	2	(2)
Effect on other comprehensive income, net of tax	1	(1)	7	1
Accumulated other comprehensive income, net of tax, end of period	(1)	(5)	(1)	(5)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	71	2,946	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	(77)	189	(378)	541
Change in pension obligations, before tax	0	1	1	2
Change in life deferred acquisition costs, life policy reserves and other, before tax	1	(2)	9	1
Effect on other comprehensive income, before tax	(76)	188	(368)	544
Accumulated other comprehensive income, before tax, end of period	(5)	3,134	(5)	3,134
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	16	1,021	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	(17)	66	(81)	189
Change in pension obligations, tax	0	1	0	1
Change in life deferred acquisition costs, life policy reserves and other, tax	0	(1)	2	0
Effect on other comprehensive income, tax	(17)	66	(79)	190
Accumulated other comprehensive income, tax, end of period	(1)	1,087	(1)	1,087
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	(4)	2,047	(4)	2,047	$ (4)	$ 55	285	$ 2,047	$ 1,925	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	(60)	123	(297)	352
Change in pension obligations, net of tax	0	0	1	1
Change in life deferred acquisition costs, life policy reserves and other, net of tax	1	(1)	7	1
Effect on other comprehensive income, net of tax	(59)	122	(289)	354
Accumulated other comprehensive income, net of tax, end of period	$ (4)	$ 2,047	(4)	2,047
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