Fair Value Measurements - Changes in Level 3 Financial Assets (Details) - Debt and Equity Securities [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 436	$ 596	$ 410	$ 732
Total gains (losses) included in shareholders' net income	0	(1)	(1)	(21)
Gains (losses) included in other comprehensive income	5	(5)	12	(10)
Gains (losses) required to adjust future policy benefits for settlement annuities	0	(2)	2	(6)
Purchases, sales, and settlements:
Purchases	43	6	43	16
Sales	0	0	0	(11)
Settlements	(9)	(13)	(10)	(15)
Total purchases, sales, settlements	34	(7)	33	(10)
Transfers into/(out of) Level 3:
Transfers into Level 3	13	0	33	20
Transfers out of Level 3	(57)	(53)	(58)	(177)
Total transfers into/(out of) Level 3	(44)	(53)	(25)	(157)
Ending Balance	431	528	431	528
Total gains (losses) included in income attributable to instruments held at the reporting date	$ (1)	$ (1)	$ (1)	(8)
Accounting Standards Update 2016-01 [Member]
Transfers into/(out of) Level 3:
Transfers out of Level 3				$ (70)