INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	$ 3,449	$ 4,528
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	364	2,213
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	25,402	31,709
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	4,239	20,347
12 months or longer Unrealized Losses	21,163	11,362
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3,085	2,315
Dollar-denominated | U.S. government and agencies
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	4	8
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	3
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	123	159
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	53	85
12 months or longer Unrealized Losses	70	74
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3	5
Dollar-denominated | Municipalities
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	38	89
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	57
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	703	854
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	31	735
12 months or longer Unrealized Losses	672	119
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	37	32
Dollar-denominated | Mortgage- and asset-backed securities
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	56	84
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	6	42
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	925	936
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	340	640
12 months or longer Unrealized Losses	585	296
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	50	42
Dollar-denominated | Public utilities
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	114	180
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4	144
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	1,120	1,852
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	228	1,667
12 months or longer Unrealized Losses	892	185
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	110	36
Dollar-denominated | Sovereign and supranational
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	8	12
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	35	30
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	0	0
12 months or longer Unrealized Losses	35	30
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	8	12
Dollar-denominated | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	51	105
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4	58
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	655	1,147
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	159	786
12 months or longer Unrealized Losses	496	361
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	47	47
Dollar-denominated | Other corporate
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	665	1,201
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	19	785
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	6,380	10,529
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	799	8,636
12 months or longer Unrealized Losses	5,581	1,893
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	646	416
Yen-denominated | Japan government and agencies
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	1,696	1,724
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	303	580
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	8,393	8,856
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	1,657	3,733
12 months or longer Unrealized Losses	6,736	5,123
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1,393	1,144
Yen-denominated | Municipalities
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	58	61
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	26
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	301	286
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	34	150
12 months or longer Unrealized Losses	267	136
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	58	35
Yen-denominated | Mortgage- and asset-backed securities
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	11	12
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	6
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	58	62
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	0	38
12 months or longer Unrealized Losses	58	24
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	11	6
Yen-denominated | Public utilities
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	82	108
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	13	61
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	1,028	880
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	444	576
12 months or longer Unrealized Losses	584	304
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	69	47
Yen-denominated | Sovereign and supranational
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	7	5
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	4
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	60	71
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	0	34
12 months or longer Unrealized Losses	60	37
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	7	1
Yen-denominated | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	365	531
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4	174
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	3,673	3,957
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	186	1,760
12 months or longer Unrealized Losses	3,487	2,197
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	361	357
Yen-denominated | Other corporate
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	294	408
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	9	273
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	1,948	2,090
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	308	1,507
12 months or longer Unrealized Losses	1,640	583
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 285	$ 135