INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Detail) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Investments, Unrealized Loss Position [Line Items]
Document Period End Date	Jun. 30, 2019
Fixed maturity securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	$ 11,427	$ 24,484
Total Unrealized Losses	727	1,760
Less than 12 months Fair Value	4,940	16,389
Less than 12 months Unrealized Losses	300	985
12 months or longer Fair Value	6,487	8,095
12 months or longer Unrealized Losses	427	775
Yen-denominated | Fixed maturity securities | 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 | Fixed maturity securities | 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 | Fixed maturity securities | 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 | Fixed maturity securities | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,862	3,057
Total Unrealized Losses	118	258
Less than 12 months Fair Value	1,862	3,057
Less than 12 months Unrealized Losses	118	258
12 months or longer Fair Value	0	0
12 months or longer Unrealized Losses	0	0
Yen-denominated | Fixed maturity securities | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	713	1,306
Total Unrealized Losses	28	82
Less than 12 months Fair Value	713	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
Dollar-denominated | Fixed maturity securities | 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 | Fixed maturity securities | 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 | Fixed maturity securities | 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 | Fixed maturity securities | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	597	1,585
Total Unrealized Losses	27	105
Less than 12 months Fair Value	116	892
Less than 12 months Unrealized Losses	5	48
12 months or longer Fair Value	481	693
12 months or longer Unrealized Losses	22	57
Dollar-denominated | Fixed maturity securities | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	284	625
Total Unrealized Losses	14	35
Less than 12 months Fair Value	110	340
Less than 12 months Unrealized Losses	5	19
12 months or longer Fair Value	174	285
12 months or longer Unrealized Losses	9	16
Dollar-denominated | Fixed maturity securities | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	7,957	12,899
Total Unrealized Losses	539	1,109
Less than 12 months Fair Value	2,125	5,782
Less than 12 months Unrealized Losses	143	407
12 months or longer Fair Value	5,832	7,117
12 months or longer Unrealized Losses	$ 396	$ 702