Closed Block (Liabilities and Assets) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Closed Block Liabilities
Future policy benefits	$ 39,477	$ 40,032
Other policy-related balances	438	317
Policyholder dividends payable	453	431
Policyholder dividend obligation	2,370	428	$ 2,121
Deferred income tax liability	61	28
Other liabilities	116	328
Total closed block liabilities	42,915	41,564
Assets Designated to the Closed Block
Fixed maturity securities available-for-sale, at estimated fair value	26,365	25,354
Equity securities, at estimated fair value	63	61
Contractholder-directed equity securities and fair value option securities, at estimated fair value	50	43
Mortgage loans	6,910	6,778
Policy loans	4,493	4,527
Real estate and real estate joint ventures	540	544
Other invested assets	822	643
Total investments	39,243	37,950
Assets Designated to Closed Block, Cash and Cash Equivalents	154	0
Accrued investment income	438	443
Premiums, reinsurance and other receivables	66	83
Current income tax recoverable	81	69
Total assets designated to the closed block	39,982	38,545
Excess of closed block liabilities over assets designated to the closed block	2,933	3,019
Amounts included in AOCI:
Unrealized investment gains (losses), net of income tax	2,596	1,089
Unrealized gains (losses) on derivatives, net of income tax	169	86
Allocated to policyholder dividend obligation, net of income tax	(1,872)	(338)
Total amounts included in AOCI	893	837
Maximum future earnings to be recognized from closed block assets and liabilities	$ 3,826	$ 3,856