INVESTMENTS - Available-for-Sale Debt Securities (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	$ 70,689	$ 75,469
Allowance for Credit Losses	0	0
Gross Unrealized Gains	6,050	4,800
Gross Unrealized Losses	3,449	4,528
Fair Value	73,290	75,741
Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	40,174	43,920
Allowance for Credit Losses	0	0
Gross Unrealized Gains	2,529	2,595
Gross Unrealized Losses	2,513	2,849
Fair Value	40,190	43,666
Dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	30,515	31,549
Allowance for Credit Losses	0	0
Gross Unrealized Gains	3,521	2,205
Gross Unrealized Losses	936	1,679
Fair Value	33,100	32,075
Japan government and agencies \| Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	23,067	25,418
Allowance for Credit Losses	0	0
Gross Unrealized Gains	1,040	1,259
Gross Unrealized Losses	1,696	1,724
Fair Value	22,411	24,953
Municipalities
Debt Securities, Available-for-Sale [Line Items]
Fair Value	2,298	2,320
Municipalities \| Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	968	1,034
Allowance for Credit Losses	0	0
Gross Unrealized Gains	115	124
Gross Unrealized Losses	58	61
Fair Value	1,025	1,097
Municipalities \| Dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	1,246	1,269
Allowance for Credit Losses	0	0
Gross Unrealized Gains	65	43
Gross Unrealized Losses	38	89
Fair Value	1,273	1,223
Mortgage- and asset-backed securities
Debt Securities, Available-for-Sale [Line Items]
Fair Value	3,086	2,146
Mortgage- and asset-backed securities \| Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	215	241
Allowance for Credit Losses	0	0
Gross Unrealized Gains	6	8
Gross Unrealized Losses	11	12
Fair Value	210	237
Mortgage- and asset-backed securities \| Dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	2,748	1,926
Allowance for Credit Losses	0	0
Gross Unrealized Gains	184	67
Gross Unrealized Losses	56	84
Fair Value	2,876	1,909
Public utilities
Debt Securities, Available-for-Sale [Line Items]
Fair Value	7,592	7,666
Public utilities \| Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	3,757	3,932
Allowance for Credit Losses	0	0
Gross Unrealized Gains	325	301
Gross Unrealized Losses	82	108
Fair Value	4,000	4,125
Public utilities \| Dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	3,346	3,481
Allowance for Credit Losses	0	0
Gross Unrealized Gains	360	240
Gross Unrealized Losses	114	180
Fair Value	3,592	3,541
Sovereign and supranational
Debt Securities, Available-for-Sale [Line Items]
Fair Value	537	834
Sovereign and supranational \| Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	373	659
Allowance for Credit Losses	0	0
Gross Unrealized Gains	24	24
Gross Unrealized Losses	7	5
Fair Value	390	678
Sovereign and supranational \| Dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	122	133
Allowance for Credit Losses	0	0
Gross Unrealized Gains	33	35
Gross Unrealized Losses	8	12
Fair Value	147	156
Banks/financial institutions
Debt Securities, Available-for-Sale [Line Items]
Fair Value	8,835	9,299
Banks/financial institutions \| Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	5,896	6,348
Allowance for Credit Losses	0	0
Gross Unrealized Gains	320	324
Gross Unrealized Losses	365	531
Fair Value	5,851	6,141
Banks/financial institutions \| Dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	2,676	2,992
Allowance for Credit Losses	0	0
Gross Unrealized Gains	359	271
Gross Unrealized Losses	51	105
Fair Value	2,984	3,158
Other corporate
Debt Securities, Available-for-Sale [Line Items]
Fair Value	28,342	28,362
Other corporate \| Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	5,898	6,288
Allowance for Credit Losses	0	0
Gross Unrealized Gains	699	555
Gross Unrealized Losses	294	408
Fair Value	6,303	6,435
Other corporate \| Dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	20,186	21,579
Allowance for Credit Losses	0	0
Gross Unrealized Gains	2,518	1,549
Gross Unrealized Losses	665	1,201
Fair Value	22,039	21,927
U.S. government and agencies \| Dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	191	169
Allowance for Credit Losses	0	0
Gross Unrealized Gains	2	0
Gross Unrealized Losses	4	8
Fair Value	$ 189	$ 161

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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