INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Detail) - Fixed maturity securities - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	$ 18,043	$ 7,190
Total Unrealized Losses	2,141	385
Less than 12 months Fair Value	14,118	3,423
Less than 12 months Unrealized Losses	1,476	178
12 months or longer Fair Value	3,925	3,767
12 months or longer Unrealized Losses	665	207
Yen-denominated | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	56	80
Total Unrealized Losses	1	3
Less than 12 months Fair Value	42	80
Less than 12 months Unrealized Losses	0	3
12 months or longer Fair Value	14	0
12 months or longer Unrealized Losses	1	0
Yen-denominated | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	880
Total Unrealized Losses	93
Less than 12 months Fair Value	880
Less than 12 months Unrealized Losses	93
12 months or longer Fair Value	0
12 months or longer Unrealized Losses	0
Yen-denominated | Sovereign and supranational
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	701
Total Unrealized Losses	27
Less than 12 months Fair Value	701
Less than 12 months Unrealized Losses	27
12 months or longer Fair Value	0
12 months or longer Unrealized Losses	0
Yen-denominated | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	3,410	1,828
Total Unrealized Losses	557	89
Less than 12 months Fair Value	2,626	1,828
Less than 12 months Unrealized Losses	406	89
12 months or longer Fair Value	784	0
12 months or longer Unrealized Losses	151	0
Yen-denominated | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	2,829	636
Total Unrealized Losses	389	31
Less than 12 months Fair Value	2,677	636
Less than 12 months Unrealized Losses	357	31
12 months or longer Fair Value	152	0
12 months or longer Unrealized Losses	32	0
Yen-denominated | Japan government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	725
Total Unrealized Losses	14
Less than 12 months Fair Value	725
Less than 12 months Unrealized Losses	14
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	825	306
Total Unrealized Losses	50	10
Less than 12 months Fair Value	701	69
Less than 12 months Unrealized Losses	38	2
12 months or longer Fair Value	124	237
12 months or longer Unrealized Losses	12	8
Dollar-denominated | Sovereign and supranational
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	18
Total Unrealized Losses	1
Less than 12 months Fair Value	18
Less than 12 months Unrealized Losses	1
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	355	79
Total Unrealized Losses	21	4
Less than 12 months Fair Value	321	18
Less than 12 months Unrealized Losses	13	0
12 months or longer Fair Value	34	61
12 months or longer Unrealized Losses	8	4
Dollar-denominated | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	8,244	4,261
Total Unrealized Losses	988	248
Less than 12 months Fair Value	5,427	792
Less than 12 months Unrealized Losses	527	53
12 months or longer Fair Value	2,817	3,469
12 months or longer Unrealized Losses	$ 461	$ 195