INVESTMENTS - Available-for-sale Debt Securities (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 70,849	$ 75,469
Allowance for Credit Losses	0	0
Gross Unrealized Gains	6,462	4,800
Gross Unrealized Losses	2,806	4,528
Fair   Value	74,505	75,741
Yen-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	40,349	43,920
Allowance for Credit Losses	0	0
Gross Unrealized Gains	3,088	2,595
Gross Unrealized Losses	1,660	2,849
Fair   Value	41,777	43,666
Dollar-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	30,500	31,549
Allowance for Credit Losses	0	0
Gross Unrealized Gains	3,374	2,205
Gross Unrealized Losses	1,146	1,679
Fair   Value	32,728	32,075
Japan government and agencies | Yen-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	23,313	25,418
Allowance for Credit Losses	0	0
Gross Unrealized Gains	1,435	1,259
Gross Unrealized Losses	975	1,724
Fair   Value	23,773	24,953
Municipalities
Debt Securities, Available-for-sale [Line Items]
Fair   Value	2,323	2,320
Municipalities | Yen-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	946	1,034
Allowance for Credit Losses	0	0
Gross Unrealized Gains	150	124
Gross Unrealized Losses	35	61
Fair   Value	1,061	1,097
Municipalities | Dollar-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,251	1,269
Allowance for Credit Losses	0	0
Gross Unrealized Gains	62	43
Gross Unrealized Losses	51	89
Fair   Value	1,262	1,223
Mortgage- and asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Fair   Value	2,855	2,146
Mortgage- and asset-backed securities | Yen-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	213	241
Allowance for Credit Losses	0	0
Gross Unrealized Gains	8	8
Gross Unrealized Losses	6	12
Fair   Value	215	237
Mortgage- and asset-backed securities | Dollar-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,521	1,926
Allowance for Credit Losses	0	0
Gross Unrealized Gains	189	67
Gross Unrealized Losses	70	84
Fair   Value	2,640	1,909
Public utilities
Debt Securities, Available-for-sale [Line Items]
Fair   Value	7,569	7,666
Public utilities | Yen-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,665	3,932
Allowance for Credit Losses	0	0
Gross Unrealized Gains	367	301
Gross Unrealized Losses	51	108
Fair   Value	3,981	4,125
Public utilities | Dollar-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,384	3,481
Allowance for Credit Losses	0	0
Gross Unrealized Gains	347	240
Gross Unrealized Losses	143	180
Fair   Value	3,588	3,541
Sovereign and supranational
Debt Securities, Available-for-sale [Line Items]
Fair   Value	674	834
Sovereign and supranational | Yen-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	498	659
Allowance for Credit Losses	0	0
Gross Unrealized Gains	34	24
Gross Unrealized Losses	4	5
Fair   Value	528	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	34	35
Gross Unrealized Losses	10	12
Fair   Value	146	156
Banks/financial institutions
Debt Securities, Available-for-sale [Line Items]
Fair   Value	8,849	9,299
Banks/financial institutions | Yen-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,767	6,348
Allowance for Credit Losses	0	0
Gross Unrealized Gains	349	324
Gross Unrealized Losses	309	531
Fair   Value	5,807	6,141
Banks/financial institutions | Dollar-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,766	2,992
Allowance for Credit Losses	0	0
Gross Unrealized Gains	346	271
Gross Unrealized Losses	70	105
Fair   Value	3,042	3,158
Other corporate
Debt Securities, Available-for-sale [Line Items]
Fair   Value	28,282	28,362
Other corporate | Yen-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,947	6,288
Allowance for Credit Losses	0	0
Gross Unrealized Gains	745	555
Gross Unrealized Losses	280	408
Fair   Value	6,412	6,435
Other corporate | Dollar-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	20,269	21,579
Allowance for Credit Losses	0	0
Gross Unrealized Gains	2,396	1,549
Gross Unrealized Losses	795	1,201
Fair   Value	21,870	21,927
U.S. government and agencies | Dollar-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	187	169
Allowance for Credit Losses	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	7	8
Fair   Value	$ 180	$ 161