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, 2018	Dec. 31, 2017
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	$ 24,484	$ 16,685
Total Unrealized Losses	[1]	1,760	813
Less Than 12 months Fair Value	[1]	16,389	5,776
Less Than 12 months Unrealized Losses	[1]	985	77
12 months or longer Fair Value	[1]	8,095	10,909
12 months or longer Unrealized Losses	[1]	775	736
Dollar-denominated | U.S. government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	67	74
Total Unrealized Losses	[1]	1	1
Less Than 12 months Fair Value	[1]	67	74
Less Than 12 months Unrealized Losses	[1]	1	1
12 months or longer Fair Value	[1]	0	0
12 months or longer Unrealized Losses	[1]	0	0
Dollar-denominated | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	515
Total Unrealized Losses	[1]	8
Less Than 12 months Fair Value	[1]	515
Less Than 12 months Unrealized Losses	[1]	8
12 months or longer Fair Value	[1]	0
12 months or longer Unrealized Losses	[1]	0
Dollar-denominated | Mortgage- and asset-backed securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	74
Total Unrealized Losses	[1]	1
Less Than 12 months Fair Value	[1]	74
Less Than 12 months Unrealized Losses	[1]	1
12 months or longer Fair Value	[1]	0
12 months or longer Unrealized Losses	[1]	0
Dollar-denominated | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	1,585	785
Total Unrealized Losses	[1]	105	27
Less Than 12 months Fair Value	[1]	892	221
Less Than 12 months Unrealized Losses	[1]	48	3
12 months or longer Fair Value	[1]	693	564
12 months or longer Unrealized Losses	[1]	57	24
Dollar-denominated | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	625	362
Total Unrealized Losses	[1]	35	8
Less Than 12 months Fair Value	[1]	340	316
Less Than 12 months Unrealized Losses	[1]	19	5
12 months or longer Fair Value	[1]	285	46
12 months or longer Unrealized Losses	[1]	16	3
Dollar-denominated | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	12,899	7,741
Total Unrealized Losses	[1]	1,109	418
Less Than 12 months Fair Value	[1]	5,782	2,839
Less Than 12 months Unrealized Losses	[1]	407	50
12 months or longer Fair Value	[1]	7,117	4,902
12 months or longer Unrealized Losses	[1]	702	368
Yen-denominated | Japan government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	3,604	5,255
Total Unrealized Losses	[1]	140	271
Less Than 12 months Fair Value	[1]	3,604	1,264
Less Than 12 months Unrealized Losses	[1]	140	9
12 months or longer Fair Value	[1]	0	3,991
12 months or longer Unrealized Losses	[1]	0	262
Yen-denominated | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	148	129
Total Unrealized Losses	[1]	9	12
Less Than 12 months Fair Value	[1]	148	10
Less Than 12 months Unrealized Losses	[1]	9	0
12 months or longer Fair Value	[1]	0	119
12 months or longer Unrealized Losses	[1]	0	12
Yen-denominated | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	604	83
Total Unrealized Losses	[1]	12	6
Less Than 12 months Fair Value	[1]	604	0
Less Than 12 months Unrealized Losses	[1]	12	0
12 months or longer Fair Value	[1]	0	83
12 months or longer Unrealized Losses	[1]	0	6
Yen-denominated | Sovereign and supranational
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]		309
Total Unrealized Losses	[1]		1
Less Than 12 months Fair Value	[1]		309
Less Than 12 months Unrealized Losses	[1]		1
12 months or longer Fair Value	[1]		0
12 months or longer Unrealized Losses	[1]		0
Yen-denominated | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	3,057	1,507
Total Unrealized Losses	[1]	258	62
Less Than 12 months Fair Value	[1]	3,057	394
Less Than 12 months Unrealized Losses	[1]	258	4
12 months or longer Fair Value	[1]	0	1,113
12 months or longer Unrealized Losses	[1]	0	58
Yen-denominated | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	1,306	440
Total Unrealized Losses	[1]	82	7
Less Than 12 months Fair Value	[1]	1,306	349
Less Than 12 months Unrealized Losses	[1]	82	4
12 months or longer Fair Value	[1]	0	91
12 months or longer Unrealized Losses	[1]	$ 0	$ 3

[1] Includes perpetual securities