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INVESTMENTS - Net Investment Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Sep. 30, 2022	Mar. 31, 2022
Net Investment Income [Line Items]
Gross investment income	$ 87		$ 103
Less: investment expenses	(11)		(4)
Net investment income	76	$ 99	99
Retained Business
Net Investment Income [Line Items]
Gross investment income	65
Less: investment expenses	(9)
Net investment income	56
Ceded Business
Net Investment Income [Line Items]
Gross investment income	22
Less: investment expenses	(2)
Net investment income	20
Fixed maturity securities
Net Investment Income [Line Items]
Gross investment income	61		61
Fixed maturity securities \| Retained Business
Net Investment Income [Line Items]
Gross investment income	47
Fixed maturity securities \| Ceded Business
Net Investment Income [Line Items]
Gross investment income	14
Equity securities
Net Investment Income [Line Items]
Gross investment income	1		1
Equity securities \| Retained Business
Net Investment Income [Line Items]
Gross investment income	0
Equity securities \| Ceded Business
Net Investment Income [Line Items]
Gross investment income	1
Mortgage and other loans
Net Investment Income [Line Items]
Gross investment income	4		11
Mortgage and other loans \| Retained Business
Net Investment Income [Line Items]
Gross investment income	4
Mortgage and other loans \| Ceded Business
Net Investment Income [Line Items]
Gross investment income	0
Other invested assets
Net Investment Income [Line Items]
Gross investment income	13		29
Other invested assets \| Retained Business
Net Investment Income [Line Items]
Gross investment income	12
Other invested assets \| Ceded Business
Net Investment Income [Line Items]
Gross investment income	1
Short-term investments and cash equivalents
Net Investment Income [Line Items]
Gross investment income	8		$ 1
Short-term investments and cash equivalents \| Retained Business
Net Investment Income [Line Items]
Gross investment income	2
Short-term investments and cash equivalents \| Ceded Business
Net Investment Income [Line Items]
Gross investment income	$ 6