INVESTMENTS - Available-for-Sale Debt Securities (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	$ 85,369	$ 91,630
Allowance for Credit Losses	0	38
Gross Unrealized Gains	13,566	14,771
Gross Unrealized Losses	239	481
Fair Value	98,696	105,882
Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	51,160	56,049
Allowance for Credit Losses	0	0
Gross Unrealized Gains	6,994	8,420
Gross Unrealized Losses	167	198
Fair Value	57,987	64,271
Dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	34,209	35,581
Allowance for Credit Losses	0	38
Gross Unrealized Gains	6,572	6,351
Gross Unrealized Losses	72	283
Fair Value	40,709	41,611
Japan government and agencies \| Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	30,335	32,959
Allowance for Credit Losses	0	0
Gross Unrealized Gains	3,343	4,182
Gross Unrealized Losses	61	52
Fair Value	33,617	37,089
U.S. government and agencies \| Dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	196	245
Allowance for Credit Losses	0	0
Gross Unrealized Gains	8	16
Gross Unrealized Losses	1	0
Fair Value	203	261
Municipalities
Debt Securities, Available-for-Sale [Line Items]
Fair Value	3,036	3,018
Municipalities \| Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	1,192	1,324
Allowance for Credit Losses	0	0
Gross Unrealized Gains	322	374
Gross Unrealized Losses	5	5
Fair Value	1,509	1,693
Municipalities \| Dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	1,340	1,154
Allowance for Credit Losses	0	0
Gross Unrealized Gains	189	173
Gross Unrealized Losses	2	2
Fair Value	1,527	1,325
Mortgage- and asset-backed securities
Debt Securities, Available-for-Sale [Line Items]
Fair Value	1,246	1,038
Mortgage- and asset-backed securities \| Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	300	342
Allowance for Credit Losses	0	0
Gross Unrealized Gains	19	27
Gross Unrealized Losses	1	1
Fair Value	318	368
Mortgage- and asset-backed securities \| Dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	897	667
Allowance for Credit Losses	0	0
Gross Unrealized Gains	33	8
Gross Unrealized Losses	2	5
Fair Value	928	670
Public utilities
Debt Securities, Available-for-Sale [Line Items]
Fair Value	10,051	10,817
Public utilities \| Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	4,462	4,777
Allowance for Credit Losses	0	0
Gross Unrealized Gains	906	1,096
Gross Unrealized Losses	2	1
Fair Value	5,366	5,872
Public utilities \| Dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	3,781	4,013
Allowance for Credit Losses	0	0
Gross Unrealized Gains	909	947
Gross Unrealized Losses	5	15
Fair Value	4,685	4,945
Sovereign and supranational
Debt Securities, Available-for-Sale [Line Items]
Fair Value	1,115	1,382
Sovereign and supranational \| Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	760	981
Allowance for Credit Losses	0	0
Gross Unrealized Gains	82	108
Gross Unrealized Losses	0	0
Fair Value	842	1,089
Sovereign and supranational \| Dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	222	232
Allowance for Credit Losses	0	0
Gross Unrealized Gains	57	64
Gross Unrealized Losses	6	3
Fair Value	273	293
Banks/financial institutions
Debt Securities, Available-for-Sale [Line Items]
Fair Value	11,591	12,060
Banks/financial institutions \| Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	6,963	7,552
Allowance for Credit Losses	0	0
Gross Unrealized Gains	787	886
Gross Unrealized Losses	72	102
Fair Value	7,678	8,336
Banks/financial institutions \| Dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	3,169	2,973
Allowance for Credit Losses	0	0
Gross Unrealized Gains	747	758
Gross Unrealized Losses	3	7
Fair Value	3,913	3,724
Other corporate
Debt Securities, Available-for-Sale [Line Items]
Fair Value	37,837	40,217
Other corporate \| Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	7,148	8,114
Allowance for Credit Losses	0	0
Gross Unrealized Gains	1,535	1,747
Gross Unrealized Losses	26	37
Fair Value	8,657	9,824
Other corporate \| Dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	24,604	26,297
Allowance for Credit Losses	0	38
Gross Unrealized Gains	4,629	4,385
Gross Unrealized Losses	53	251
Fair Value	$ 29,180	$ 30,393

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 of 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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