Closed Block (Liabilities and Assets) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Closed Block Liabilities
Future policy benefits	$ 38,191	$ 38,758
Other policy-related balances	289	321
Policyholder dividends payable	299	337
Policyholder dividend obligation	1,952	2,969	$ 2,020
Deferred income tax liability	175	130
Other liabilities	269	172
Total closed block liabilities	41,175	42,687
Assets Designated to the Closed Block
Fixed maturity securities available-for-sale, at estimated fair value	25,977	27,186
Equity securities, at estimated fair value	21	24
Mortgage loans	6,441	6,807
Policy loans	4,235	4,355
Real estate and real estate joint ventures	575	559
Other invested assets	540	468
Total investments	37,789	39,399
Cash and cash equivalents	173	0
Accrued investment income	391	402
Premiums, reinsurance and other receivables	40	50
Current income tax recoverable	52	28
Total assets designated to the closed block	38,445	39,879
Excess of closed block liabilities over assets designated to the closed block	2,730	2,808
AOCI:
Unrealized investment gains (losses), net of income tax	2,730	3,524
Unrealized gains (losses) on derivatives, net of income tax	100	23
Allocated to policyholder dividend obligation, net of income tax	(1,542)	(2,346)
Total amounts included in AOCI	1,288	1,201
Maximum future earnings to be recognized from closed block assets and liabilities	$ 4,018	$ 4,009