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, 2018	Dec. 31, 2017
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	$ 28,469	$ 16,685
Total Unrealized Losses	[1]	1,565	813
Less than 12 months Fair Value	[1]	27,989	5,776
Less than 12 months Unrealized Losses	[1]	1,533	77
12 months or longer Fair Value	[1]	480	10,909
12 months or longer Unrealized Losses	[1]	32	736
Dollar-denominated | U.S. government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	80	74
Total Unrealized Losses	[1]	1	1
Less than 12 months Fair Value	[1]	80	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]	490
Total Unrealized Losses	[1]	12
Less than 12 months Fair Value	[1]	490
Less than 12 months Unrealized Losses	[1]	12
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]	81
Total Unrealized Losses	[1]	1
Less than 12 months Fair Value	[1]	81
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]	1,726	785
Total Unrealized Losses	[1]	91	27
Less than 12 months Fair Value	[1]	1,721	221
Less than 12 months Unrealized Losses	[1]	91	3
12 months or longer Fair Value	[1]	5	564
12 months or longer Unrealized Losses	[1]	0	24
Dollar-denominated | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	552	362
Total Unrealized Losses	[1]	19	8
Less than 12 months Fair Value	[1]	517	316
Less than 12 months Unrealized Losses	[1]	18	5
12 months or longer Fair Value	[1]	35	46
12 months or longer Unrealized Losses	[1]	1	3
Dollar-denominated | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	11,731	7,741
Total Unrealized Losses	[1]	775	418
Less than 12 months Fair Value	[1]	11,291	2,839
Less than 12 months Unrealized Losses	[1]	744	50
12 months or longer Fair Value	[1]	440	4,902
12 months or longer Unrealized Losses	[1]	31	368
Yen-denominated | Japan government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	9,221	5,255
Total Unrealized Losses	[1]	426	271
Less than 12 months Fair Value	[1]	9,221	1,264
Less than 12 months Unrealized Losses	[1]	426	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]	224	129
Total Unrealized Losses	[1]	17	12
Less than 12 months Fair Value	[1]	224	10
Less than 12 months Unrealized Losses	[1]	17	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]	381	83
Total Unrealized Losses	[1]	10	6
Less than 12 months Fair Value	[1]	381	0
Less than 12 months Unrealized Losses	[1]	10	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]	43	309
Total Unrealized Losses	[1]	1	1
Less than 12 months Fair Value	[1]	43	309
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
Yen-denominated | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	2,806	1,507
Total Unrealized Losses	[1]	170	62
Less than 12 months Fair Value	[1]	2,806	394
Less than 12 months Unrealized Losses	[1]	170	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]	1,134	440
Total Unrealized Losses	[1]	42	7
Less than 12 months Fair Value	[1]	1,134	349
Less than 12 months Unrealized Losses	[1]	42	4
12 months or longer Fair Value	[1]	0	91
12 months or longer Unrealized Losses	[1]	$ 0	$ 3

[1] Includes perpetual securities