INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Detail) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Fixed maturity securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	$ 7,946	$ 10,781
Total Unrealized Losses	235	481
Less than 12 months Fair Value	2,609	6,902
Less than 12 months Unrealized Losses	31	184
12 months or Longer Fair Value	5,337	3,879
12 months or Longer Unrealized Losses	204	297
Yen-denominated | Fixed maturity securities | Japan government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	2,980	2,604
Total Unrealized Losses	62	52
Less than 12 months Fair Value	342	2,604
Less than 12 months Unrealized Losses	2	52
12 months or Longer Fair Value	2,638	0
12 months or Longer Unrealized Losses	60	0
Yen-denominated | Fixed maturity securities | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	168	183
Total Unrealized Losses	5	5
Less than 12 months Fair Value	30	169
Less than 12 months Unrealized Losses	0	4
12 months or Longer Fair Value	138	14
12 months or Longer Unrealized Losses	5	1
Yen-denominated | Fixed maturity securities | Mortgage- and asset-backed securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	34	37
Total Unrealized Losses	1	1
Less than 12 months Fair Value	0	37
Less than 12 months Unrealized Losses	0	1
12 months or Longer Fair Value	34	0
12 months or Longer Unrealized Losses	1	0
Yen-denominated | Fixed maturity securities | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	242	135
Total Unrealized Losses	2	1
Less than 12 months Fair Value	182	135
Less than 12 months Unrealized Losses	1	1
12 months or Longer Fair Value	60	0
12 months or Longer Unrealized Losses	1	0
Yen-denominated | Fixed maturity securities | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	558	613
Total Unrealized Losses	22	37
Less than 12 months Fair Value	106	290
Less than 12 months Unrealized Losses	1	13
12 months or Longer Fair Value	452	323
12 months or Longer Unrealized Losses	21	24
Yen-denominated | Fixed maturity securities | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,824	1,809
Total Unrealized Losses	66	102
Less than 12 months Fair Value	735	765
Less than 12 months Unrealized Losses	5	36
12 months or Longer Fair Value	1,089	1,044
12 months or Longer Unrealized Losses	61	66
Dollar-denominated | Fixed maturity securities | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	56	94
Total Unrealized Losses	1	2
Less than 12 months Fair Value	56	94
Less than 12 months Unrealized Losses	1	2
12 months or Longer Fair Value	0	0
12 months or Longer Unrealized Losses	0	0
Dollar-denominated | Fixed maturity securities | Mortgage- and asset-backed securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		360
Total Unrealized Losses		5
Less than 12 months Fair Value		360
Less than 12 months Unrealized Losses		5
12 months or Longer Fair Value		0
12 months or Longer Unrealized Losses		0
Dollar-denominated | Fixed maturity securities | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	195	326
Total Unrealized Losses	4	15
Less than 12 months Fair Value	108	208
Less than 12 months Unrealized Losses	2	7
12 months or Longer Fair Value	87	118
12 months or Longer Unrealized Losses	2	8
Dollar-denominated | Fixed maturity securities | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,731	4,499
Total Unrealized Losses	67	251
Less than 12 months Fair Value	898	2,157
Less than 12 months Unrealized Losses	17	59
12 months or Longer Fair Value	833	2,342
12 months or Longer Unrealized Losses	50	192
Dollar-denominated | Fixed maturity securities | Sovereign and supranational
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	6	39
Total Unrealized Losses	4	3
Less than 12 months Fair Value	6	39
Less than 12 months Unrealized Losses	1	3
12 months or Longer Fair Value	0	0
12 months or Longer Unrealized Losses	3	0
Dollar-denominated | Fixed maturity securities | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	152	82
Total Unrealized Losses	1	7
Less than 12 months Fair Value	146	44
Less than 12 months Unrealized Losses	1	1
12 months or Longer Fair Value	6	38
12 months or Longer Unrealized Losses	$ 0	$ 6