INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Detail) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-Sale, Unrealized Loss Position, Total	$ 24,301	$ 25,402
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	4,128	3,449
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	6,716	4,239
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	197	364
12 months or longer Unrealized Losses	17,585	21,163
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3,931	3,085
U.S. dollar-denominated | U.S. government and agencies
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-Sale, Unrealized Loss Position, Total	106	123
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	3	4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	59	53
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	1
12 months or longer Unrealized Losses	47	70
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2	3
U.S. dollar-denominated | Municipalities
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-Sale, Unrealized Loss Position, Total	666	703
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	53	38
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	67	31
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3	1
12 months or longer Unrealized Losses	599	672
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	50	37
U.S. dollar-denominated | Mortgage- and asset-backed securities
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-Sale, Unrealized Loss Position, Total	567	925
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	34	56
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	173	340
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2	6
12 months or longer Unrealized Losses	394	585
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	32	50
U.S. dollar-denominated | Public utilities
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-Sale, Unrealized Loss Position, Total	1,570	1,120
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	151	114
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	699	228
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	19	4
12 months or longer Unrealized Losses	871	892
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	132	110
U.S. dollar-denominated | Sovereign and supranational
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-Sale, Unrealized Loss Position, Total		35
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total		8
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months		0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		0
12 months or longer Unrealized Losses		35
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		8
U.S. dollar-denominated | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-Sale, Unrealized Loss Position, Total	625	655
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	36	51
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	376	159
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	7	4
12 months or longer Unrealized Losses	249	496
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	29	47
U.S. dollar-denominated | Other corporate
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-Sale, Unrealized Loss Position, Total	6,097	6,380
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	752	665
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	2,036	799
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	59	19
12 months or longer Unrealized Losses	4,061	5,581
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	693	646
Yen-denominated | Japan government and agencies
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-Sale, Unrealized Loss Position, Total	8,136	8,393
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	2,234	1,696
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	2,070	1,657
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	57	303
12 months or longer Unrealized Losses	6,066	6,736
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,177	1,393
Yen-denominated | Municipalities
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-Sale, Unrealized Loss Position, Total	341	301
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	79	58
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	96	34
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2	0
12 months or longer Unrealized Losses	245	267
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	77	58
Yen-denominated | Mortgage- and asset-backed securities
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-Sale, Unrealized Loss Position, Total	196	58
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	23	11
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	12	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
12 months or longer Unrealized Losses	184	58
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	23	11
Yen-denominated | Public utilities
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-Sale, Unrealized Loss Position, Total	1,020	1,028
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	108	82
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	368	444
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	11	13
12 months or longer Unrealized Losses	652	584
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	97	69
Yen-denominated | Sovereign and supranational
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-Sale, Unrealized Loss Position, Total	47	60
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	8	7
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
12 months or longer Unrealized Losses	47	60
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	8	7
Yen-denominated | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-Sale, Unrealized Loss Position, Total	3,197	3,673
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	342	365
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	471	186
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	22	4
12 months or longer Unrealized Losses	2,726	3,487
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	320	361
Yen-denominated | Other corporate
Investments, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-Sale, Unrealized Loss Position, Total	1,733	1,948
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	305	294
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	289	308
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	14	9
12 months or longer Unrealized Losses	1,444	1,640
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 291	$ 285