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, 2019	Dec. 31, 2018
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	$ 13,416	$ 24,484
Total Unrealized Losses	823	1,760
Less than 12 months Fair Value	6,745	16,389
Less than 12 months Unrealized Losses	417	985
12 months or longer Fair Value	6,671	8,095
12 months or longer Unrealized Losses	406	775
Dollar-denominated | U.S. government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	65	67
Total Unrealized Losses	1	1
Less than 12 months Fair Value	65	67
Less than 12 months Unrealized Losses	1	1
12 months or longer Fair Value	0	0
12 months or longer Unrealized Losses	0	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	53	74
Total Unrealized Losses	0	1
Less than 12 months Fair Value	53	74
Less than 12 months Unrealized Losses	0	1
12 months or longer Fair Value	0	0
12 months or longer Unrealized Losses	0	0
Dollar-denominated | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	808	1,585
Total Unrealized Losses	32	105
Less than 12 months Fair Value	306	892
Less than 12 months Unrealized Losses	14	48
12 months or longer Fair Value	502	693
12 months or longer Unrealized Losses	18	57
Dollar-denominated | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	345	625
Total Unrealized Losses	13	35
Less than 12 months Fair Value	209	340
Less than 12 months Unrealized Losses	10	19
12 months or longer Fair Value	136	285
12 months or longer Unrealized Losses	3	16
Dollar-denominated | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	9,182	12,899
Total Unrealized Losses	598	1,109
Less than 12 months Fair Value	3,149	5,782
Less than 12 months Unrealized Losses	213	407
12 months or longer Fair Value	6,033	7,117
12 months or longer Unrealized Losses	385	702
Yen-denominated | Japan government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	139	3,604
Total Unrealized Losses	2	140
Less than 12 months Fair Value	139	3,604
Less than 12 months Unrealized Losses	2	140
12 months or longer Fair Value	0	0
12 months or longer Unrealized Losses	0	0
Yen-denominated | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	70	148
Total Unrealized Losses	3	9
Less than 12 months Fair Value	70	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	2,229	3,057
Total Unrealized Losses	149	258
Less than 12 months Fair Value	2,229	3,057
Less than 12 months Unrealized Losses	149	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	525	1,306
Total Unrealized Losses	25	82
Less than 12 months Fair Value	525	1,306
Less than 12 months Unrealized Losses	25	82
12 months or longer Fair Value	0	0
12 months or longer Unrealized Losses	$ 0	$ 0