INVESTMENTS - Securities Lending Transactions Accounted for as Secured Borrowings (Details) - USD ($) $ in Millions		Sep. 30, 2024	Dec. 31, 2023
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred		$ 4,233	$ 1,503
Gross amount of recognized liabilities for securities lending		4,233	1,503
Japan government and agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred		3,179	737
Public utilities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred		52	19
Banks/financial institutions
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred		133	72
Other corporate
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred		869	675
Maturity Overnight and Continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred	[1]	1,054	766
Maturity Overnight and Continuous | Japan government and agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred	[1]	0	0
Maturity Overnight and Continuous | Public utilities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred	[1]	52	19
Maturity Overnight and Continuous | Banks/financial institutions
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred	[1]	133	72
Maturity Overnight and Continuous | Other corporate
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred	[1]	869	675
Maturity up to 30 Days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred		3,179	737
Maturity up to 30 Days | Japan government and agencies
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred		3,179	737
Maturity up to 30 Days | Public utilities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred		0	0
Maturity up to 30 Days | Banks/financial institutions
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred		0	0
Maturity up to 30 Days | Other corporate
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred		$ 0	$ 0

[1] The related loaned security, under the Company's U.S. securities lending program, can be returned to the Company at the transferee's discretion; therefore, they are classified as Overnight and Continuous.