INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Detail) - Fixed maturity securities - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	$ 7,190	$ 24,484
Total Unrealized Losses	385	1,760
Less Than 12 months Fair Value	3,423	16,389
Less Than 12 months Unrealized Losses	178	985
12 months or longer Fair Value	3,767	8,095
12 months or longer Unrealized Losses	207	775
Yen-denominated | Japan government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		3,604
Total Unrealized Losses		140
Less Than 12 months Fair Value		3,604
Less Than 12 months Unrealized Losses		140
12 months or longer Fair Value		0
12 months or longer Unrealized Losses		0
Yen-denominated | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	80	148
Total Unrealized Losses	3	9
Less Than 12 months Fair Value	80	148
Less Than 12 months Unrealized Losses	3	9
12 months or longer Fair Value	0	0
12 months or longer Unrealized Losses	0	0
Yen-denominated | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		604
Total Unrealized Losses		12
Less Than 12 months Fair Value		604
Less Than 12 months Unrealized Losses		12
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	1,828	3,057
Total Unrealized Losses	89	258
Less Than 12 months Fair Value	1,828	3,057
Less Than 12 months Unrealized Losses	89	258
12 months or longer Fair Value	0	0
12 months or longer Unrealized Losses	0	0
Yen-denominated | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	636	1,306
Total Unrealized Losses	31	82
Less Than 12 months Fair Value	636	1,306
Less Than 12 months Unrealized Losses	31	82
12 months or longer Fair Value	0	0
12 months or longer Unrealized Losses	0	0
Dollar-denominated | U.S. government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		67
Total Unrealized Losses		1
Less Than 12 months Fair Value		67
Less Than 12 months Unrealized Losses		1
12 months or longer Fair Value		0
12 months or longer Unrealized Losses		0
Dollar-denominated | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		515
Total Unrealized Losses		8
Less Than 12 months Fair Value		515
Less Than 12 months Unrealized Losses		8
12 months or longer Fair Value		0
12 months or longer Unrealized Losses		0
Dollar-denominated | Mortgage- and asset-backed securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		74
Total Unrealized Losses		1
Less Than 12 months Fair Value		74
Less Than 12 months Unrealized Losses		1
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	306	1,585
Total Unrealized Losses	10	105
Less Than 12 months Fair Value	69	892
Less Than 12 months Unrealized Losses	2	48
12 months or longer Fair Value	237	693
12 months or longer Unrealized Losses	8	57
Dollar-denominated | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	79	625
Total Unrealized Losses	4	35
Less Than 12 months Fair Value	18	340
Less Than 12 months Unrealized Losses	0	19
12 months or longer Fair Value	61	285
12 months or longer Unrealized Losses	4	16
Dollar-denominated | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	4,261	12,899
Total Unrealized Losses	248	1,109
Less Than 12 months Fair Value	792	5,782
Less Than 12 months Unrealized Losses	53	407
12 months or longer Fair Value	3,469	7,117
12 months or longer Unrealized Losses	$ 195	$ 702