INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	$ 24,604	$ 25,402
Total Unrealized Losses	3,875	3,449
Less than 12 months Fair Value	4,814	4,239
Less than 12 months Unrealized Losses	342	364
12 months or Longer Fair Value	19,790	21,163
12 months or Longer Unrealized Losses	3,533	3,085
Dollar-denominated | U.S. government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	76	123
Total Unrealized Losses	1	4
Less than 12 months Fair Value	27	53
Less than 12 months Unrealized Losses	0	1
12 months or Longer Fair Value	49	70
12 months or Longer Unrealized Losses	1	3
Dollar-denominated | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	636	703
Total Unrealized Losses	32	38
Less than 12 months Fair Value	8	31
Less than 12 months Unrealized Losses	0	1
12 months or Longer Fair Value	628	672
12 months or Longer Unrealized Losses	32	37
Dollar-denominated | Mortgage- and asset-backed securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	999	925
Total Unrealized Losses	47	56
Less than 12 months Fair Value	580	340
Less than 12 months Unrealized Losses	20	6
12 months or Longer Fair Value	419	585
12 months or Longer Unrealized Losses	27	50
Dollar-denominated | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,256	1,120
Total Unrealized Losses	98	114
Less than 12 months Fair Value	369	228
Less than 12 months Unrealized Losses	9	4
12 months or Longer Fair Value	887	892
12 months or Longer Unrealized Losses	89	110
Dollar-denominated | Sovereign and supranational
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		35
Total Unrealized Losses		8
Less than 12 months Fair Value		0
Less than 12 months Unrealized Losses		0
12 months or Longer Fair Value		35
12 months or Longer Unrealized Losses		8
Dollar-denominated | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	716	655
Total Unrealized Losses	23	51
Less than 12 months Fair Value	419	159
Less than 12 months Unrealized Losses	3	4
12 months or Longer Fair Value	297	496
12 months or Longer Unrealized Losses	20	47
Dollar-denominated | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	6,079	6,380
Total Unrealized Losses	497	665
Less than 12 months Fair Value	1,579	799
Less than 12 months Unrealized Losses	31	19
12 months or Longer Fair Value	4,500	5,581
12 months or Longer Unrealized Losses	466	646
Yen-denominated | Japan government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	8,088	8,393
Total Unrealized Losses	2,322	1,696
Less than 12 months Fair Value	874	1,657
Less than 12 months Unrealized Losses	230	303
12 months or Longer Fair Value	7,214	6,736
12 months or Longer Unrealized Losses	2,092	1,393
Yen-denominated | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	289	301
Total Unrealized Losses	77	58
Less than 12 months Fair Value	10	34
Less than 12 months Unrealized Losses	0	0
12 months or Longer Fair Value	279	267
12 months or Longer Unrealized Losses	77	58
Yen-denominated | Mortgage- and asset-backed securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	208	58
Total Unrealized Losses	22	11
Less than 12 months Fair Value	0	0
Less than 12 months Unrealized Losses	0	0
12 months or Longer Fair Value	208	58
12 months or Longer Unrealized Losses	22	11
Yen-denominated | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	910	1,028
Total Unrealized Losses	116	82
Less than 12 months Fair Value	304	444
Less than 12 months Unrealized Losses	32	13
12 months or Longer Fair Value	606	584
12 months or Longer Unrealized Losses	84	69
Yen-denominated | Sovereign and supranational
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	56	60
Total Unrealized Losses	8	7
Less than 12 months Fair Value	0	0
Less than 12 months Unrealized Losses	0	0
12 months or Longer Fair Value	56	60
12 months or Longer Unrealized Losses	8	7
Yen-denominated | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	3,484	3,673
Total Unrealized Losses	332	365
Less than 12 months Fair Value	431	186
Less than 12 months Unrealized Losses	10	4
12 months or Longer Fair Value	3,053	3,487
12 months or Longer Unrealized Losses	322	361
Yen-denominated | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,807	1,948
Total Unrealized Losses	300	294
Less than 12 months Fair Value	213	308
Less than 12 months Unrealized Losses	7	9
12 months or Longer Fair Value	1,594	1,640
12 months or Longer Unrealized Losses	$ 293	$ 285