INVESTMENTS - Available-for-Sale Debt Securities (Detail) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	$ 65,263	$ 64,089
Allowance for Credit Losses	0	0	$ 0	$ 0
Gross Unrealized Gains	4,782	5,308
Gross Unrealized Losses	5,924	4,128
Fair Value	64,121	65,269
Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	32,885	34,386
Allowance for Credit Losses	0	0
Gross Unrealized Gains	704	1,587
Gross Unrealized Losses	5,108	3,099
Fair Value	28,481	32,874
U.S. dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	32,257	29,678
Allowance for Credit Losses	0	0
Gross Unrealized Gains	4,068	3,720
Gross Unrealized Losses	816	1,029
Fair Value	35,509	32,369
Other currencies
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	121	25
Allowance for Credit Losses	0	0
Gross Unrealized Gains	10	1
Gross Unrealized Losses	0	0
Fair Value	131	26
Japan government and agencies | Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	18,063	19,409
Allowance for Credit Losses	0	0
Gross Unrealized Gains	41	465
Gross Unrealized Losses	3,727	2,234
Fair Value	14,377	17,640
Municipalities
Debt Securities, Available-for-Sale [Line Items]
Fair Value	1,930	2,034
Municipalities | Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	856	869
Allowance for Credit Losses	0	0
Gross Unrealized Gains	5	65
Gross Unrealized Losses	145	79
Fair Value	716	855
Municipalities | U.S. dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	1,185	1,167
Allowance for Credit Losses	0	0
Gross Unrealized Gains	83	65
Gross Unrealized Losses	54	53
Fair Value	1,214	1,179
Mortgage- and asset-backed securities
Debt Securities, Available-for-Sale [Line Items]
Fair Value	4,366	3,563
Mortgage- and asset-backed securities | Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	297	327
Allowance for Credit Losses	0	0
Gross Unrealized Gains	1	4
Gross Unrealized Losses	38	23
Fair Value	260	308
Mortgage- and asset-backed securities | U.S. dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	3,854	2,987
Allowance for Credit Losses	0	0
Gross Unrealized Gains	239	302
Gross Unrealized Losses	35	34
Fair Value	4,058	3,255
Mortgage- and asset-backed securities | Other currencies
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	44
Allowance for Credit Losses	0
Gross Unrealized Gains	4
Gross Unrealized Losses	0
Fair Value	48
Public utilities
Debt Securities, Available-for-Sale [Line Items]
Fair Value	7,174	7,045
Public utilities | Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	2,519	2,746
Allowance for Credit Losses	0	0
Gross Unrealized Gains	123	202
Gross Unrealized Losses	174	108
Fair Value	2,468	2,840
Public utilities | U.S. dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	4,292	3,938
Allowance for Credit Losses	0	0
Gross Unrealized Gains	465	418
Gross Unrealized Losses	107	151
Fair Value	4,650	4,205
Public utilities | Other currencies
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	52
Allowance for Credit Losses	0
Gross Unrealized Gains	4
Gross Unrealized Losses	0
Fair Value	56
Sovereign and supranational
Debt Securities, Available-for-Sale [Line Items]
Fair Value	402	416
Sovereign and supranational | Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	330	330
Allowance for Credit Losses	0	0
Gross Unrealized Gains	7	16
Gross Unrealized Losses	13	8
Fair Value	324	338
Sovereign and supranational | U.S. dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	57	57
Allowance for Credit Losses	0	0
Gross Unrealized Gains	21	21
Gross Unrealized Losses	0	0
Fair Value	78	78
Banks/financial institutions
Debt Securities, Available-for-Sale [Line Items]
Fair Value	9,244	8,956
Banks/financial institutions | Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	5,382	5,376
Allowance for Credit Losses	0	0
Gross Unrealized Gains	170	267
Gross Unrealized Losses	477	342
Fair Value	5,075	5,301
Banks/financial institutions | U.S. dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	3,672	3,271
Allowance for Credit Losses	0	0
Gross Unrealized Gains	518	420
Gross Unrealized Losses	21	36
Fair Value	4,169	3,655
Other corporate
Debt Securities, Available-for-Sale [Line Items]
Fair Value	26,398	25,409
Other corporate | Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	5,438	5,329
Allowance for Credit Losses	0	0
Gross Unrealized Gains	357	568
Gross Unrealized Losses	534	305
Fair Value	5,261	5,592
Other corporate | U.S. dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	18,967	18,050
Allowance for Credit Losses	0	0
Gross Unrealized Gains	2,740	2,493
Gross Unrealized Losses	597	752
Fair Value	21,110	19,791
Other corporate | Other currencies
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	25	25
Allowance for Credit Losses	0	0
Gross Unrealized Gains	2	1
Gross Unrealized Losses	0	0
Fair Value	27	26
U.S. government and agencies | U.S. dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	230	208
Allowance for Credit Losses	0	0
Gross Unrealized Gains	2	1
Gross Unrealized Losses	2	3
Fair Value	$ 230	$ 206