INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Detail) - Fixed maturity securities - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	$ 8,246	$ 24,484
Total Unrealized Losses	552	1,760
Less than 12 months Fair Value	3,813	16,389
Less than 12 months Unrealized Losses	266	985
12 months or longer Fair Value	4,433	8,095
12 months or longer Unrealized Losses	286	775
Yen-denominated | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	14	148
Total Unrealized Losses	1	9
Less than 12 months Fair Value	14	148
Less than 12 months Unrealized Losses	1	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	1,795	3,057
Total Unrealized Losses	106	258
Less than 12 months Fair Value	1,795	3,057
Less than 12 months Unrealized Losses	106	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	462	1,306
Total Unrealized Losses	28	82
Less than 12 months Fair Value	462	1,306
Less than 12 months Unrealized Losses	28	82
12 months or longer Fair Value	0	0
12 months or longer Unrealized Losses	0	0
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
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 | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	305	1,585
Total Unrealized Losses	12	105
Less than 12 months Fair Value	58	892
Less than 12 months Unrealized Losses	2	48
12 months or longer Fair Value	247	693
12 months or longer Unrealized Losses	10	57
Dollar-denominated | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	223	625
Total Unrealized Losses	8	35
Less than 12 months Fair Value	115	340
Less than 12 months Unrealized Losses	5	19
12 months or longer Fair Value	108	285
12 months or longer Unrealized Losses	3	16
Dollar-denominated | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	5,447	12,899
Total Unrealized Losses	397	1,109
Less than 12 months Fair Value	1,369	5,782
Less than 12 months Unrealized Losses	124	407
12 months or longer Fair Value	4,078	7,117
12 months or longer Unrealized Losses	$ 273	702
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 | 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