INVESTMENTS - Held-to-Maturity Debt Securities (Details) - USD ($) $ in Millions	Sep. 30, 2025		Jun. 30, 2025	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Dec. 31, 2023
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 16,960			$ 15,971
Allowance for Credit Loss	5		$ 5	5	$ 5	$ 5	$ 5
Total fixed maturity securities, held-to-maturity, amortized cost	16,955	[1]		15,966
Gross Unrealized Gains	260			815
Gross Unrealized Losses	445			9
Fair Value	16,770			16,772
Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	16,960			15,971
Allowance for Credit Loss	5			5
Total fixed maturity securities, held-to-maturity, amortized cost	16,955			15,966
Gross Unrealized Gains	260			815
Gross Unrealized Losses	445			9
Fair Value	16,770			16,772
Japan government and agencies | Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	16,260			15,311
Allowance for Credit Loss	2			2
Total fixed maturity securities, held-to-maturity, amortized cost	16,258			15,309
Gross Unrealized Gains	248			759
Gross Unrealized Losses	438			9
Fair Value	16,068			16,059
Municipalities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	248			235
Fair Value	252			257
Municipalities | Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	248			235
Allowance for Credit Loss	0			0
Total fixed maturity securities, held-to-maturity, amortized cost	248			235
Gross Unrealized Gains	5			22
Gross Unrealized Losses	1			0
Fair Value	252			257
Public utilities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	34			32
Fair Value	32			33
Public utilities | Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	34			32
Allowance for Credit Loss	0			0
Total fixed maturity securities, held-to-maturity, amortized cost	34			32
Gross Unrealized Gains	0			1
Gross Unrealized Losses	2			0
Fair Value	32			33
Sovereign and supranational
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	398			374
Fair Value	400			405
Sovereign and supranational | Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	401			377
Allowance for Credit Loss	3			3
Total fixed maturity securities, held-to-maturity, amortized cost	398			374
Gross Unrealized Gains	6			31
Gross Unrealized Losses	4			0
Fair Value	400			405
Other corporate
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	17			16
Fair Value	18			18
Other corporate | Yen-denominated
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	17			16
Allowance for Credit Loss	0			0
Total fixed maturity securities, held-to-maturity, amortized cost	17			16
Gross Unrealized Gains	1			2
Gross Unrealized Losses	0			0
Fair Value	$ 18			$ 18

[1] Net of allowance for credit losses