INVESTMENTS - Available-for-Sale Debt Securities (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	$ 75,469	$ 85,369
Allowance for Credit Losses	0	0
Gross Unrealized Gains	4,800	13,566
Gross Unrealized Losses	4,528	239
Fair Value	75,741	98,696
Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	43,920	51,160
Allowance for Credit Losses	0	0
Gross Unrealized Gains	2,595	6,994
Gross Unrealized Losses	2,849	167
Fair Value	43,666	57,987
Dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	31,549	34,209
Allowance for Credit Losses	0	0
Gross Unrealized Gains	2,205	6,572
Gross Unrealized Losses	1,679	72
Fair Value	32,075	40,709
Japan government and agencies \| Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	25,418	30,335
Allowance for Credit Losses	0	0
Gross Unrealized Gains	1,259	3,343
Gross Unrealized Losses	1,724	61
Fair Value	24,953	33,617
Municipalities
Debt Securities, Available-for-Sale [Line Items]
Fair Value	2,320	3,036
Municipalities \| Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	1,034	1,192
Allowance for Credit Losses	0	0
Gross Unrealized Gains	124	322
Gross Unrealized Losses	61	5
Fair Value	1,097	1,509
Municipalities \| Dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	1,269	1,340
Allowance for Credit Losses	0	0
Gross Unrealized Gains	43	189
Gross Unrealized Losses	89	2
Fair Value	1,223	1,527
Mortgage- and asset-backed securities
Debt Securities, Available-for-Sale [Line Items]
Fair Value	2,146	1,246
Mortgage- and asset-backed securities \| Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	241	300
Allowance for Credit Losses	0	0
Gross Unrealized Gains	8	19
Gross Unrealized Losses	12	1
Fair Value	237	318
Mortgage- and asset-backed securities \| Dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	1,926	897
Allowance for Credit Losses	0	0
Gross Unrealized Gains	67	33
Gross Unrealized Losses	84	2
Fair Value	1,909	928
Public utilities
Debt Securities, Available-for-Sale [Line Items]
Fair Value	7,666	10,051
Public utilities \| Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	3,932	4,462
Allowance for Credit Losses	0	0
Gross Unrealized Gains	301	906
Gross Unrealized Losses	108	2
Fair Value	4,125	5,366
Public utilities \| Dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	3,481	3,781
Allowance for Credit Losses	0	0
Gross Unrealized Gains	240	909
Gross Unrealized Losses	180	5
Fair Value	3,541	4,685
Sovereign and supranational
Debt Securities, Available-for-Sale [Line Items]
Fair Value	834	1,115
Sovereign and supranational \| Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	659	760
Allowance for Credit Losses	0	0
Gross Unrealized Gains	24	82
Gross Unrealized Losses	5	0
Fair Value	678	842
Sovereign and supranational \| Dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	133	222
Allowance for Credit Losses	0	0
Gross Unrealized Gains	35	57
Gross Unrealized Losses	12	6
Fair Value	156	273
Banks/financial institutions
Debt Securities, Available-for-Sale [Line Items]
Fair Value	9,299	11,591
Banks/financial institutions \| Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	6,348	6,963
Allowance for Credit Losses	0	0
Gross Unrealized Gains	324	787
Gross Unrealized Losses	531	72
Fair Value	6,141	7,678
Banks/financial institutions \| Dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	2,992	3,169
Allowance for Credit Losses	0	0
Gross Unrealized Gains	271	747
Gross Unrealized Losses	105	3
Fair Value	3,158	3,913
Other corporate
Debt Securities, Available-for-Sale [Line Items]
Fair Value	28,362	37,837
Other corporate \| Yen-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	6,288	7,148
Allowance for Credit Losses	0	0
Gross Unrealized Gains	555	1,535
Gross Unrealized Losses	408	26
Fair Value	6,435	8,657
Other corporate \| Dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	21,579	24,604
Allowance for Credit Losses	0	0
Gross Unrealized Gains	1,549	4,629
Gross Unrealized Losses	1,201	53
Fair Value	21,927	29,180
U.S. government and agencies \| Dollar-denominated
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	169	196
Allowance for Credit Losses	0	0
Gross Unrealized Gains	0	8
Gross Unrealized Losses	8	1
Fair Value	$ 161	$ 203

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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