INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	$ 16,766	$ 20,275
Total Unrealized Losses	816	1,156
Less Than 12 months Fair Value	5,836	14,743
Less Than 12 months Unrealized Losses	78	621
12 months or longer Fair Value	10,930	5,532
12 months or longer Unrealized Losses	738	535
Fixed maturities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	16,340	19,536
Total Unrealized Losses	786	1,099
Less Than 12 months Fair Value	5,776	14,398
Less Than 12 months Unrealized Losses	77	612
12 months or longer Fair Value	10,564	5,138
12 months or longer Unrealized Losses	709	487
Perpetual securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	345	479
Total Unrealized Losses	27	49
Less Than 12 months Fair Value	0	85
Less Than 12 months Unrealized Losses	0	1
12 months or longer Fair Value	345	394
12 months or longer Unrealized Losses	27	48
Equity securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	81	260
Total Unrealized Losses	3	8
Less Than 12 months Fair Value	60	260
Less Than 12 months Unrealized Losses	1	8
12 months or longer Fair Value	21	0
12 months or longer Unrealized Losses	2	0
Dollar-denominated | Fixed maturities | U.S. Government and Agencies
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 maturities | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		44
Total Unrealized Losses		8
Less Than 12 months Fair Value		0
Less Than 12 months Unrealized Losses		0
12 months or longer Fair Value		44
12 months or longer Unrealized Losses		8
Dollar-denominated | Fixed maturities | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	785	1,265
Total Unrealized Losses	27	60
Less Than 12 months Fair Value	221	790
Less Than 12 months Unrealized Losses	3	32
12 months or longer Fair Value	564	475
12 months or longer Unrealized Losses	24	28
Dollar-denominated | Fixed maturities | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	362	268
Total Unrealized Losses	8	16
Less Than 12 months Fair Value	316	238
Less Than 12 months Unrealized Losses	5	10
12 months or longer Fair Value	46	30
12 months or longer Unrealized Losses	3	6
Dollar-denominated | Fixed maturities | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	7,741	10,462
Total Unrealized Losses	418	690
Less Than 12 months Fair Value	2,839	7,252
Less Than 12 months Unrealized Losses	50	346
12 months or longer Fair Value	4,902	3,210
12 months or longer Unrealized Losses	368	344
Dollar-denominated | Equity securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	41	211
Total Unrealized Losses	2	6
Less Than 12 months Fair Value	21	211
Less Than 12 months Unrealized Losses	0	6
12 months or longer Fair Value	20	0
12 months or longer Unrealized Losses	2	0
Yen-denominated | Fixed maturities | Japan government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	5,255	3,958
Total Unrealized Losses	271	160
Less Than 12 months Fair Value	1,264	3,958
Less Than 12 months Unrealized Losses	9	160
12 months or longer Fair Value	3,991	0
12 months or longer Unrealized Losses	262	0
Yen-denominated | Fixed maturities | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	129	105
Total Unrealized Losses	12	8
Less Than 12 months Fair Value	10	105
Less Than 12 months Unrealized Losses	0	8
12 months or longer Fair Value	119	0
12 months or longer Unrealized Losses	12	0
Yen-denominated | Fixed maturities | Mortgage- and asset-backed securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		713
Total Unrealized Losses		8
Less Than 12 months Fair Value		713
Less Than 12 months Unrealized Losses		8
12 months or longer Fair Value		0
12 months or longer Unrealized Losses		0
Yen-denominated | Fixed maturities | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	83	635
Total Unrealized Losses	6	26
Less Than 12 months Fair Value	0	347
Less Than 12 months Unrealized Losses	0	14
12 months or longer Fair Value	83	288
12 months or longer Unrealized Losses	6	12
Yen-denominated | Fixed maturities | Sovereign and supranational
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	309	244
Total Unrealized Losses	1	13
Less Than 12 months Fair Value	309	38
Less Than 12 months Unrealized Losses	1	5
12 months or longer Fair Value	0	206
12 months or longer Unrealized Losses	0	8
Yen-denominated | Fixed maturities | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,162	1,521
Total Unrealized Losses	35	100
Less Than 12 months Fair Value	394	636
Less Than 12 months Unrealized Losses	4	19
12 months or longer Fair Value	768	885
12 months or longer Unrealized Losses	31	81
Yen-denominated | Fixed maturities | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	440	321
Total Unrealized Losses	7	10
Less Than 12 months Fair Value	349	321
Less Than 12 months Unrealized Losses	4	10
12 months or longer Fair Value	91	0
12 months or longer Unrealized Losses	3	0
Yen-denominated | Perpetual securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	345	479
Total Unrealized Losses	27	49
Less Than 12 months Fair Value	0	85
Less Than 12 months Unrealized Losses	0	1
12 months or longer Fair Value	345	394
12 months or longer Unrealized Losses	27	48
Yen-denominated | Equity securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	40	49
Total Unrealized Losses	1	2
Less Than 12 months Fair Value	39	49
Less Than 12 months Unrealized Losses	1	2
12 months or longer Fair Value	1	0
12 months or longer Unrealized Losses	$ 0	$ 0