INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Detail) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	$ 24,554	$ 25,402
Total Unrealized Losses	4,315	3,449
Less than 12 months Fair Value	6,609	4,239
Less than 12 months Unrealized Losses	708	364
12 months or Longer Fair Value	17,945	21,163
12 months or Longer Unrealized Losses	3,607	3,085
Dollar-denominated | U.S. government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	114	123
Total Unrealized Losses	4	4
Less than 12 months Fair Value	38	53
Less than 12 months Unrealized Losses	1	1
12 months or Longer Fair Value	76	70
12 months or Longer Unrealized Losses	3	3
Dollar-denominated | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	670	703
Total Unrealized Losses	49	38
Less than 12 months Fair Value	29	31
Less than 12 months Unrealized Losses	1	1
12 months or Longer Fair Value	641	672
12 months or Longer Unrealized Losses	48	37
Dollar-denominated | Mortgage- and asset-backed securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	684	925
Total Unrealized Losses	44	56
Less than 12 months Fair Value	167	340
Less than 12 months Unrealized Losses	1	6
12 months or Longer Fair Value	517	585
12 months or Longer Unrealized Losses	43	50
Dollar-denominated | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,438	1,120
Total Unrealized Losses	150	114
Less than 12 months Fair Value	445	228
Less than 12 months Unrealized Losses	15	4
12 months or Longer Fair Value	993	892
12 months or Longer Unrealized Losses	135	110
Dollar-denominated | Sovereign and supranational
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	14	35
Total Unrealized Losses	3	8
Less than 12 months Fair Value	0	0
Less than 12 months Unrealized Losses	0	0
12 months or Longer Fair Value	14	35
12 months or Longer Unrealized Losses	3	8
Dollar-denominated | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	753	655
Total Unrealized Losses	50	51
Less than 12 months Fair Value	345	159
Less than 12 months Unrealized Losses	8	4
12 months or Longer Fair Value	408	496
12 months or Longer Unrealized Losses	42	47
Dollar-denominated | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	6,336	6,380
Total Unrealized Losses	823	665
Less than 12 months Fair Value	1,473	799
Less than 12 months Unrealized Losses	43	19
12 months or Longer Fair Value	4,863	5,581
12 months or Longer Unrealized Losses	780	646
Yen-denominated | Japan government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	8,156	8,393
Total Unrealized Losses	2,376	1,696
Less than 12 months Fair Value	2,577	1,657
Less than 12 months Unrealized Losses	574	303
12 months or Longer Fair Value	5,579	6,736
12 months or Longer Unrealized Losses	1,802	1,393
Yen-denominated | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	339	301
Total Unrealized Losses	74	58
Less than 12 months Fair Value	123	34
Less than 12 months Unrealized Losses	4	0
12 months or Longer Fair Value	216	267
12 months or Longer Unrealized Losses	70	58
Yen-denominated | Mortgage- and asset-backed securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	223	58
Total Unrealized Losses	22	11
Less than 12 months Fair Value	41	0
Less than 12 months Unrealized Losses	0	0
12 months or Longer Fair Value	182	58
12 months or Longer Unrealized Losses	22	11
Yen-denominated | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	951	1,028
Total Unrealized Losses	94	82
Less than 12 months Fair Value	492	444
Less than 12 months Unrealized Losses	18	13
12 months or Longer Fair Value	459	584
12 months or Longer Unrealized Losses	76	69
Yen-denominated | Sovereign and supranational
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	25	60
Total Unrealized Losses	7	7
Less than 12 months Fair Value	0	0
Less than 12 months Unrealized Losses	1	0
12 months or Longer Fair Value	25	60
12 months or Longer Unrealized Losses	6	7
Yen-denominated | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	3,132	3,673
Total Unrealized Losses	332	365
Less than 12 months Fair Value	450	186
Less than 12 months Unrealized Losses	23	4
12 months or Longer Fair Value	2,682	3,487
12 months or Longer Unrealized Losses	309	361
Yen-denominated | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,719	1,948
Total Unrealized Losses	287	294
Less than 12 months Fair Value	429	308
Less than 12 months Unrealized Losses	19	9
12 months or Longer Fair Value	1,290	1,640
12 months or Longer Unrealized Losses	$ 268	$ 285