INVESTMENTS - Available-for-sale Debt Securities (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 69,161	$ 75,469
Allowance for Credit Losses	0	0
Gross Unrealized Gains	5,061	4,800
Gross Unrealized Losses	4,421	4,528
Fair Value	69,801	75,741
Yen-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	39,132	43,920
Allowance for Credit Losses	0	0
Gross Unrealized Gains	2,173	2,595
Gross Unrealized Losses	2,636	2,849
Fair Value	38,669	43,666
Dollar-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	30,029	31,549
Allowance for Credit Losses	0	0
Gross Unrealized Gains	2,888	2,205
Gross Unrealized Losses	1,785	1,679
Fair Value	31,132	32,075
Japan government and agencies \| Yen-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	22,605	25,418
Allowance for Credit Losses	0	0
Gross Unrealized Gains	863	1,259
Gross Unrealized Losses	1,695	1,724
Fair Value	21,773	24,953
Municipalities
Debt Securities, Available-for-sale [Line Items]
Fair Value	2,141	2,320
Municipalities \| Yen-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	918	1,034
Allowance for Credit Losses	0	0
Gross Unrealized Gains	105	124
Gross Unrealized Losses	58	61
Fair Value	965	1,097
Municipalities \| Dollar-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,241	1,269
Allowance for Credit Losses	0	0
Gross Unrealized Gains	47	43
Gross Unrealized Losses	112	89
Fair Value	1,176	1,223
Mortgage- and asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Fair Value	2,996	2,146
Mortgage- and asset-backed securities \| Yen-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	206	241
Allowance for Credit Losses	0	0
Gross Unrealized Gains	6	8
Gross Unrealized Losses	11	12
Fair Value	201	237
Mortgage- and asset-backed securities \| Dollar-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,641	1,926
Allowance for Credit Losses	0	0
Gross Unrealized Gains	228	67
Gross Unrealized Losses	74	84
Fair Value	2,795	1,909
Public utilities
Debt Securities, Available-for-sale [Line Items]
Fair Value	7,250	7,666
Public utilities \| Yen-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,652	3,932
Allowance for Credit Losses	0	0
Gross Unrealized Gains	292	301
Gross Unrealized Losses	89	108
Fair Value	3,855	4,125
Public utilities \| Dollar-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,342	3,481
Allowance for Credit Losses	0	0
Gross Unrealized Gains	291	240
Gross Unrealized Losses	238	180
Fair Value	3,395	3,541
Sovereign and supranational
Debt Securities, Available-for-sale [Line Items]
Fair Value	511	834
Sovereign and supranational \| Yen-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	355	659
Allowance for Credit Losses	0	0
Gross Unrealized Gains	19	24
Gross Unrealized Losses	6	5
Fair Value	368	678
Sovereign and supranational \| Dollar-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	121	133
Allowance for Credit Losses	0	0
Gross Unrealized Gains	31	35
Gross Unrealized Losses	9	12
Fair Value	143	156
Banks/financial institutions
Debt Securities, Available-for-sale [Line Items]
Fair Value	8,341	9,299
Banks/financial institutions \| Yen-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,561	6,348
Allowance for Credit Losses	0	0
Gross Unrealized Gains	301	324
Gross Unrealized Losses	403	531
Fair Value	5,459	6,141
Banks/financial institutions \| Dollar-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,696	2,992
Allowance for Credit Losses	0	0
Gross Unrealized Gains	285	271
Gross Unrealized Losses	99	105
Fair Value	2,882	3,158
Other corporate
Debt Securities, Available-for-sale [Line Items]
Fair Value	26,610	28,362
Other corporate \| Yen-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,835	6,288
Allowance for Credit Losses	0	0
Gross Unrealized Gains	587	555
Gross Unrealized Losses	374	408
Fair Value	6,048	6,435
Other corporate \| Dollar-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	19,799	21,579
Allowance for Credit Losses	0	0
Gross Unrealized Gains	2,006	1,549
Gross Unrealized Losses	1,243	1,201
Fair Value	20,562	21,927
U.S. government and agencies \| Dollar-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	189	169
Allowance for Credit Losses	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	10	8
Fair Value	$ 179	$ 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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