INVESTMENTS - Realized Investment Gains (Losses), Net (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Sep. 30, 2022	Mar. 31, 2022
Net Investment Income [Line Items]
Unrealized gains (losses) on investments	$ 184
Realized gains (losses) on investments	(19)
Investment gains, net	165	$ 481	$ 481
Retained Business
Net Investment Income [Line Items]
Unrealized gains (losses) on investments	156
Realized gains (losses) on investments	(126)
Investment gains, net	30
Ceded Business
Net Investment Income [Line Items]
Unrealized gains (losses) on investments	28
Realized gains (losses) on investments	107
Investment gains, net	135
Fixed maturity securities
Net Investment Income [Line Items]
Unrealized gains (losses) on investments	177
Realized gains (losses) on investments	(26)
Investment gains, net	151
Fixed maturity securities | Retained Business
Net Investment Income [Line Items]
Unrealized gains (losses) on investments	156
Realized gains (losses) on investments	(26)
Investment gains, net	130
Fixed maturity securities | Ceded Business
Net Investment Income [Line Items]
Unrealized gains (losses) on investments	21
Realized gains (losses) on investments	0
Investment gains, net	21
Equity securities
Net Investment Income [Line Items]
Unrealized gains (losses) on investments	7
Realized gains (losses) on investments	0
Investment gains, net	7		(21)
Equity securities | Retained Business
Net Investment Income [Line Items]
Unrealized gains (losses) on investments	0
Realized gains (losses) on investments	0
Investment gains, net	0
Equity securities | Ceded Business
Net Investment Income [Line Items]
Unrealized gains (losses) on investments	7
Realized gains (losses) on investments	0
Investment gains, net	7
Derivative instruments
Net Investment Income [Line Items]
Unrealized gains (losses) on investments	0
Realized gains (losses) on investments	7
Investment gains, net	7		$ 502
Derivative instruments | Retained Business
Net Investment Income [Line Items]
Unrealized gains (losses) on investments	0
Realized gains (losses) on investments	(100)
Investment gains, net	(100)
Derivative instruments | Ceded Business
Net Investment Income [Line Items]
Unrealized gains (losses) on investments	0
Realized gains (losses) on investments	107
Investment gains, net	$ 107