INVESTMENTS - Available-for-sale Debt Securities (Details) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 74,546	$ 85,369
Allowance for Credit Losses	0	0
Gross Unrealized Gains	7,326	13,566
Gross Unrealized Losses	2,441	239
Fair Value	79,431	98,696
Yen-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	42,836	51,160
Allowance for Credit Losses	0	0
Gross Unrealized Gains	3,674	6,994
Gross Unrealized Losses	1,525	167
Fair Value	44,985	57,987
Dollar-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	31,710	34,209
Allowance for Credit Losses	0	0
Gross Unrealized Gains	3,652	6,572
Gross Unrealized Losses	916	72
Fair Value	34,446	40,709
Japan government and agencies \| Yen-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	24,916	30,335
Allowance for Credit Losses	0	0
Gross Unrealized Gains	1,770	3,343
Gross Unrealized Losses	903	61
Fair Value	25,783	33,617
Municipalities
Debt Securities, Available-for-sale [Line Items]
Fair Value	2,468	3,036
Municipalities \| Yen-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,003	1,192
Allowance for Credit Losses	0	0
Gross Unrealized Gains	195	322
Gross Unrealized Losses	32	5
Fair Value	1,166	1,509
Municipalities \| Dollar-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,274	1,340
Allowance for Credit Losses	0	0
Gross Unrealized Gains	76	189
Gross Unrealized Losses	48	2
Fair Value	1,302	1,527
Mortgage- and asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Fair Value	1,952	1,246
Mortgage- and asset-backed securities \| Yen-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	245	300
Allowance for Credit Losses	0	0
Gross Unrealized Gains	11	19
Gross Unrealized Losses	6	1
Fair Value	250	318
Mortgage- and asset-backed securities \| Dollar-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,670	897
Allowance for Credit Losses	0	0
Gross Unrealized Gains	85	33
Gross Unrealized Losses	53	2
Fair Value	1,702	928
Public utilities
Debt Securities, Available-for-sale [Line Items]
Fair Value	7,957	10,051
Public utilities \| Yen-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,816	4,462
Allowance for Credit Losses	0	0
Gross Unrealized Gains	375	906
Gross Unrealized Losses	52	2
Fair Value	4,139	5,366
Public utilities \| Dollar-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,495	3,781
Allowance for Credit Losses	0	0
Gross Unrealized Gains	414	909
Gross Unrealized Losses	91	5
Fair Value	3,818	4,685
Sovereign and supranational
Debt Securities, Available-for-sale [Line Items]
Fair Value	913	1,115
Sovereign and supranational \| Yen-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	639	760
Allowance for Credit Losses	0	0
Gross Unrealized Gains	44	82
Gross Unrealized Losses	2	0
Fair Value	681	842
Sovereign and supranational \| Dollar-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	196	222
Allowance for Credit Losses	0	0
Gross Unrealized Gains	48	57
Gross Unrealized Losses	12	6
Fair Value	232	273
Banks/financial institutions
Debt Securities, Available-for-sale [Line Items]
Fair Value	9,625	11,591
Banks/financial institutions \| Yen-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	6,081	6,963
Allowance for Credit Losses	0	0
Gross Unrealized Gains	421	787
Gross Unrealized Losses	343	72
Fair Value	6,159	7,678
Banks/financial institutions \| Dollar-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,091	3,169
Allowance for Credit Losses	0	0
Gross Unrealized Gains	437	747
Gross Unrealized Losses	62	3
Fair Value	3,466	3,913
Other corporate
Debt Securities, Available-for-sale [Line Items]
Fair Value	30,557	37,837
Other corporate \| Yen-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	6,136	7,148
Allowance for Credit Losses	0	0
Gross Unrealized Gains	858	1,535
Gross Unrealized Losses	187	26
Fair Value	6,807	8,657
Other corporate \| Dollar-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	21,804	24,604
Allowance for Credit Losses	0	0
Gross Unrealized Gains	2,591	4,629
Gross Unrealized Losses	645	53
Fair Value	23,750	29,180
U.S. government and agencies \| Dollar-denominated
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	180	196
Allowance for Credit Losses	0	0
Gross Unrealized Gains	1	8
Gross Unrealized Losses	5	1
Fair Value	$ 176	$ 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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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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Amount of allowance for credit loss 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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