INVESTMENTS - Held-to-Maturity Debt Securities (Details) - USD ($) $ in Millions	Mar. 31, 2024		Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 16,694		$ 17,824
Allowance for Credit Loss	5		5	$ 6	$ 7
Total fixed maturity securities, held-to- maturity, amortized cost	16,689	[1]	17,819
Gross Unrealized Gains	1,556		1,838
Gross Unrealized Losses	0		0
Fair   Value	18,245		19,657
Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	16,694		17,824
Allowance for Credit Loss	5		5
Total fixed maturity securities, held-to- maturity, amortized cost	16,689		17,819
Gross Unrealized Gains	1,556		1,838
Gross Unrealized Losses	0		0
Fair   Value	18,245		19,657
Japan government and agencies | Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	16,002		17,085
Allowance for Credit Loss	2		2
Total fixed maturity securities, held-to- maturity, amortized cost	16,000		17,083
Gross Unrealized Gains	1,474		1,746
Gross Unrealized Losses	0		0
Fair   Value	17,474		18,829
Municipalities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	248		266
Fair   Value	285		307
Municipalities | Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	248		266
Allowance for Credit Loss	0		0
Total fixed maturity securities, held-to- maturity, amortized cost	248		266
Gross Unrealized Gains	37		41
Gross Unrealized Losses	0		0
Fair   Value	285		307
Public utilities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	33		34
Fair   Value	36		38
Public utilities | Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	33		34
Allowance for Credit Loss	0		0
Total fixed maturity securities, held-to- maturity, amortized cost	33		34
Gross Unrealized Gains	3		4
Gross Unrealized Losses	0		0
Fair   Value	36		38
Sovereign and supranational
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	391		418
Fair   Value	431		462
Sovereign and supranational | Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	394		421
Allowance for Credit Loss	3		3
Total fixed maturity securities, held-to- maturity, amortized cost	391		418
Gross Unrealized Gains	40		44
Gross Unrealized Losses	0		0
Fair   Value	431		462
Other corporate
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	17		18
Fair   Value	19		21
Other corporate | Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	17		18
Allowance for Credit Loss	0		0
Total fixed maturity securities, held-to- maturity, amortized cost	17		18
Gross Unrealized Gains	2		3
Gross Unrealized Losses	0		0
Fair   Value	$ 19		$ 21

[1] Net of allowance for credit losses