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INVESTMENTS - Net Investment Income (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2022	Dec. 31, 2023	Dec. 31, 2021
Net Investment Income [Line Items]
Gross investment income	$ 103	$ 259	$ 371	$ 517
Less: investment expense	(4)	(4)	(56)	(27)
Net investment income	99	255	315	490
Retained Business
Net Investment Income [Line Items]
Gross investment income		127	293
Less: investment expense		(2)	(53)
Net investment income		125	240
Ceded Business
Net Investment Income [Line Items]
Gross investment income		132	78
Less: investment expense		(2)	(3)
Net investment income		130	75
Fixed maturity securities
Net Investment Income [Line Items]
Gross investment income	61	217	272	383
Fixed maturity securities \| Retained Business
Net Investment Income [Line Items]
Gross investment income		123	221
Fixed maturity securities \| Ceded Business
Net Investment Income [Line Items]
Gross investment income		94	51
Equity securities
Net Investment Income [Line Items]
Gross investment income	1	3	5	5
Equity securities \| Retained Business
Net Investment Income [Line Items]
Gross investment income		0	0
Equity securities \| Ceded Business
Net Investment Income [Line Items]
Gross investment income		3	5
Secured receivable
Net Investment Income [Line Items]
Gross investment income		18	0
Secured receivable \| Retained Business
Net Investment Income [Line Items]
Gross investment income		0	0
Secured receivable \| Ceded Business
Net Investment Income [Line Items]
Gross investment income		18	0
Mortgage loans
Net Investment Income [Line Items]
Gross investment income	11	2	23	65
Mortgage loans \| Retained Business
Net Investment Income [Line Items]
Gross investment income		2	23
Mortgage loans \| Ceded Business
Net Investment Income [Line Items]
Gross investment income		0	0
Other invested assets
Net Investment Income [Line Items]
Gross investment income	29	9	29	63
Other invested assets \| Retained Business
Net Investment Income [Line Items]
Gross investment income		2	27
Other invested assets \| Ceded Business
Net Investment Income [Line Items]
Gross investment income		7	2
Short-term investments and cash equivalents
Net Investment Income [Line Items]
Gross investment income	$ 1	10	42	$ 1
Short-term investments and cash equivalents \| Retained Business
Net Investment Income [Line Items]
Gross investment income		0	22
Short-term investments and cash equivalents \| Ceded Business
Net Investment Income [Line Items]
Gross investment income		$ 10	20
Repurchase agreements \| Retained Business
Net Investment Income [Line Items]
Less: investment expense			$ (33)