Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 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	$ 55		$ 55		55		$ 2,788
Accumulated other comprehensive income, net of tax, end of period	55		55
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	164	$ 2,756	385	$ 2,625
Cumulative effect of change in accounting for equity securities, before tax							(3,155)			$ 0
Other comprehensive income before reclassification, before tax	(78)	211	(295)	501
Reclassification adjustment, before tax	(2)	10	(6)	(149)
Effect on other comprehensive income, before tax	(80)	221	(301)	352
Accumulated other comprehensive income, before tax, end of period	84	2,977	84	2,977
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	35	954	81	908
Cumulative effect of change in accounting for equity securities, tax							(652)			0
Other comprehensive income before reclassification, tax	(18)	74	(63)	176
Reclassification adjustment, tax	0	3	(1)	(53)
Effect on other comprehensive income, tax	(18)	77	(64)	123
Accumulated other comprehensive income, tax, end of period	17	1,031	17	1,031
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	67	1,946	67	1,946	67	$ 129	304	1,946	$ 1,802	1,717
Cumulative effect of change in accounting for equity securities, net										0
Other comprehensive income before reclassification, net of tax	(60)	137	(232)	325
Reclassification adjustment, net of tax	(2)	7	(5)	(96)
Effect on other comprehensive income, net of tax	(62)	144	(237)	229
Accumulated other comprehensive income, net of tax, end of period	67	1,946	67	1,946
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	(12)	(25)	(12)	(26)
Other comprehensive income before reclassification, before tax	0	0	0	0
Reclassification adjustment, before tax	1	0	1	1
Effect on other comprehensive income, before tax	1	0	1	1
Accumulated other comprehensive income, before tax, end of period	(11)	(25)	(11)	(25)
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	0	0	0
Effect on other comprehensive income, tax	0	0	0	0
Accumulated other comprehensive income, tax, end of period	(1)	(8)	(1)	(8)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	(10)	(17)	(10)	(17)	(10)	(11)	(11)	(17)	(17)	(18)
Other comprehensive income before reclassification, net of tax	0	0	0	0
Reclassification adjustment, net of tax	1	0	1	1
Effect on other comprehensive income, net of tax	1	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	(4)	(7)	(10)	(9)
Other comprehensive income before reclassification, before tax	0	0	6	3
Reclassification adjustment, before tax	2	1	2	0
Effect on other comprehensive income, before tax	2	1	8	3
Accumulated other comprehensive income, before tax, end of period	(2)	(6)	(2)	(6)
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	(1)	(2)	(2)	(3)
Other comprehensive income before reclassification, tax	0	(1)	1	1
Reclassification adjustment, tax	1	1	1	0
Effect on other comprehensive income, tax	1	0	2	1
Accumulated other comprehensive income, tax, end of period	0	(2)	0	(2)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	(2)	(4)	(2)	(4)	(2)	(3)	(8)	(4)	(5)	(6)
Other comprehensive income before reclassification, net of tax	0	1	5	2
Reclassification adjustment, net of tax	1	0	1	0
Effect on other comprehensive income, net of tax	1	1	6	2
Accumulated other comprehensive income, net of tax, end of period	(2)	(4)	(2)	(4)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before tax, beginning of period	148	2,724	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	(80)	221	(301)	352
Change in pension obligations, before tax	1	0	1	1
Change in life deferred acquisition costs, life policy reserves and other, before tax	2	1	8	3
Effect on other comprehensive income, before tax	(77)	222	(292)	356
Accumulated other comprehensive income, before tax, end of period	71	2,946	71	2,946
Accumulated Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	33	944	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	(18)	77	(64)	123
Change in pension obligations, tax	0	0	0	0
Change in life deferred acquisition costs, life policy reserves and other, tax	1	0	2	1
Effect on other comprehensive income, tax	(17)	77	(62)	124
Accumulated other comprehensive income, tax, end of period	16	1,021	16	1,021
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	55	1,925	55	1,925	$ 55	$ 115	285	$ 1,925	$ 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	(62)	144	(237)	229
Change in pension obligations, net of tax	1	0	1	1
Change in life deferred acquisition costs, life policy reserves and other, net of tax	1	1	6	2
Effect on other comprehensive income, net of tax	(60)	145	(230)	232
Accumulated other comprehensive income, net of tax, end of period	$ 55	$ 1,925	55	1,925
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