Closed Block (Liabilities and Assets) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Closed Block Liabilities
Future policy benefits	$ 39,214	$ 39,379
Other policy-related balances	340	423
Policyholder dividends payable	431	432
Policyholder dividend obligation	1,677	2,020	$ 428
Deferred income tax liability	82	79
Other liabilities	169	81
Total closed block liabilities	41,913	42,414
Assets Designated to the Closed Block
Fixed maturity securities available-for-sale, at estimated fair value	25,332	25,977
Equity securities, at estimated fair value	44	49
Contractholder-directed equity securities and fair value option securities, at estimated fair value	46	53
Mortgage loans	6,995	7,052
Policy loans	4,478	4,489
Real estate and real estate joint ventures	556	544
Other invested assets	844	314
Total investments	38,295	38,478
Cash and cash equivalents	148	448
Accrued investment income	427	419
Premiums, reinsurance and other receivables	67	75
Current income tax recoverable	90	91
Total assets designated to the closed block	39,027	39,511
Excess of closed block liabilities over assets designated to the closed block	2,886	2,903
AOCI:
Unrealized investment gains (losses), net of income tax	2,008	2,453
Unrealized gains (losses) on derivatives, net of income tax	314	97
Allocated to policyholder dividend obligation, net of income tax	(1,325)	(1,596)
Total amounts included in AOCI	997	954
Maximum future earnings to be recognized from closed block assets and liabilities	$ 3,883	$ 3,857