Fair Value Measurements - Changes in Level 3 Financial Assets and Financial Liabilities Carried at Fair Value (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Transfers into/(out of) Level 3
Change in unrealized gains or losses included in other comprehensive income for assets held at the end of the reporting period	$ (66)
Debt and Equity Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 1,	555	$ 410	$ 410
Total (losses) included in shareholders’ net income	(12)	(1)
Gains (losses) included in other comprehensive income	(71)	7
Gains (losses) required to adjust future policy benefits for settlement annuities	(10)	2
Purchases, sales and settlements
Purchases	62	0
Sales	(12)	0
Settlements	(2)	(1)
Total purchases, sales and settlements	48	(1)
Transfers into/(out of) Level 3
Transfers into Level 3	348	20
Transfers out of Level 3	(92)	(1)
Total transfers into/(out of) Level 3	256	19
Balance at March 31,	766	436	$ 555
Total (losses) included in shareholders’ net income attributable to instruments held at the reporting date	$ (18)	$ (1)