INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Detail) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 31, 2018	Dec. 31, 2017
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	$ 22,577	$ 16,685
Total Unrealized Losses	[1]	1,585	813
Less than 12 months Fair Value	[1]	12,087	5,776
Less than 12 months Unrealized Losses	[1]	549	77
12 months or longer Fair Value	[1]	10,490	10,909
12 months or longer Unrealized Losses	[1]	1,036	736
Dollar-denominated | Fixed maturities | U.S. government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	79	74
Total Unrealized Losses	[1]	1	1
Less than 12 months Fair Value	[1]	71	74
Less than 12 months Unrealized Losses	[1]	1	1
12 months or longer Fair Value	[1]	8	0
12 months or longer Unrealized Losses	[1]	0	0
Dollar-denominated | Fixed maturities | Mortgage- and asset-backed securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	91
Total Unrealized Losses	[1]	1
Less than 12 months Fair Value	[1]	71
Less than 12 months Unrealized Losses	[1]	1
12 months or longer Fair Value	[1]	20
12 months or longer Unrealized Losses	[1]	0
Dollar-denominated | Fixed maturities | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	1,649	785
Total Unrealized Losses	[1]	107	27
Less than 12 months Fair Value	[1]	1,095	221
Less than 12 months Unrealized Losses	[1]	52	3
12 months or longer Fair Value	[1]	554	564
12 months or longer Unrealized Losses	[1]	55	24
Dollar-denominated | Fixed maturities | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	685	362
Total Unrealized Losses	[1]	34	8
Less than 12 months Fair Value	[1]	596	316
Less than 12 months Unrealized Losses	[1]	28	5
12 months or longer Fair Value	[1]	89	46
12 months or longer Unrealized Losses	[1]	6	3
Dollar-denominated | Fixed maturities | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	13,730	7,741
Total Unrealized Losses	[1]	1,111	418
Less than 12 months Fair Value	[1]	8,903	2,839
Less than 12 months Unrealized Losses	[1]	420	50
12 months or longer Fair Value	[1]	4,827	4,902
12 months or longer Unrealized Losses	[1]	691	368
Yen-denominated | Fixed maturities | Japan government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	4,054	5,255
Total Unrealized Losses	[1]	192	271
Less than 12 months Fair Value	[1]	128	1,264
Less than 12 months Unrealized Losses	[1]	0	9
12 months or longer Fair Value	[1]	3,926	3,991
12 months or longer Unrealized Losses	[1]	192	262
Yen-denominated | Fixed maturities | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	128	129
Total Unrealized Losses	[1]	11	12
Less than 12 months Fair Value	[1]	0	10
Less than 12 months Unrealized Losses	[1]	0	0
12 months or longer Fair Value	[1]	128	119
12 months or longer Unrealized Losses	[1]	11	12
Yen-denominated | Fixed maturities | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	90	83
Total Unrealized Losses	[1]	4	6
Less than 12 months Fair Value	[1]	0	0
Less than 12 months Unrealized Losses	[1]	0	0
12 months or longer Fair Value	[1]	90	83
12 months or longer Unrealized Losses	[1]	4	6
Yen-denominated | Fixed maturities | Sovereign and supranational
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	302	309
Total Unrealized Losses	[1]	27	1
Less than 12 months Fair Value	[1]	302	309
Less than 12 months Unrealized Losses	[1]	27	1
12 months or longer Fair Value	[1]	0	0
12 months or longer Unrealized Losses	[1]	0	0
Yen-denominated | Fixed maturities | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	1,467	1,507
Total Unrealized Losses	[1]	89	62
Less than 12 months Fair Value	[1]	645	394
Less than 12 months Unrealized Losses	[1]	14	4
12 months or longer Fair Value	[1]	822	1,113
12 months or longer Unrealized Losses	[1]	75	58
Yen-denominated | Fixed maturities | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	[1]	302	440
Total Unrealized Losses	[1]	8	7
Less than 12 months Fair Value	[1]	276	349
Less than 12 months Unrealized Losses	[1]	6	4
12 months or longer Fair Value	[1]	26	91
12 months or longer Unrealized Losses	[1]	$ 2	$ 3

[1] Includes perpetual securities