INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Detail) - Fixed maturity securities - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	$ 8,695	$ 10,781
Total Unrealized Losses	249	481
Less than 12 months Fair Value	4,978	6,902
Less than 12 months Unrealized Losses	58	184
12 months or longer Fair Value	3,717	3,879
12 months or longer Unrealized Losses	191	297
Yen-denominated | Japan government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	3,974	2,604
Total Unrealized Losses	78	52
Less than 12 months Fair Value	3,279	2,604
Less than 12 months Unrealized Losses	32	52
12 months or longer Fair Value	695	0
12 months or longer Unrealized Losses	46	0
Yen-denominated | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	194	183
Total Unrealized Losses	7	5
Less than 12 months Fair Value	81	169
Less than 12 months Unrealized Losses	2	4
12 months or longer Fair Value	113	14
12 months or longer Unrealized Losses	5	1
Yen-denominated | 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 | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	232	135
Total Unrealized Losses	2	1
Less than 12 months Fair Value	181	135
Less than 12 months Unrealized Losses	1	1
12 months or longer Fair Value	51	0
12 months or longer Unrealized Losses	1	0
Yen-denominated | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,361	1,809
Total Unrealized Losses	65	102
Less than 12 months Fair Value	207	765
Less than 12 months Unrealized Losses	1	36
12 months or longer Fair Value	1,154	1,044
12 months or longer Unrealized Losses	64	66
Yen-denominated | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	588	613
Total Unrealized Losses	23	37
Less than 12 months Fair Value	141	290
Less than 12 months Unrealized Losses	2	13
12 months or longer Fair Value	447	323
12 months or longer Unrealized Losses	21	24
Dollar-denominated | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	38	94
Total Unrealized Losses	1	2
Less than 12 months Fair Value	37	94
Less than 12 months Unrealized Losses	1	2
12 months or longer Fair Value	1	0
12 months or longer Unrealized Losses	0	0
Dollar-denominated | 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 | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	175	326
Total Unrealized Losses	4	15
Less than 12 months Fair Value	88	208
Less than 12 months Unrealized Losses	1	7
12 months or longer Fair Value	87	118
12 months or longer Unrealized Losses	3	8
Dollar-denominated | Sovereign and supranational
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		39
Total Unrealized Losses		3
Less than 12 months Fair Value		39
Less than 12 months Unrealized Losses		3
12 months or longer Fair Value		0
12 months or longer Unrealized Losses		0
Dollar-denominated | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	103	82
Total Unrealized Losses	2	7
Less than 12 months Fair Value	81	44
Less than 12 months Unrealized Losses	1	1
12 months or longer Fair Value	22	38
12 months or longer Unrealized Losses	1	6
Dollar-denominated | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,996	4,499
Total Unrealized Losses	66	251
Less than 12 months Fair Value	883	2,157
Less than 12 months Unrealized Losses	17	59
12 months or longer Fair Value	1,113	2,342
12 months or longer Unrealized Losses	$ 49	$ 192