INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	$ 18,466	$ 20,275
Total Unrealized Losses	1,093	1,156
Less than 12 months Fair Value	11,031	14,743
Less than 12 months Unrealized Losses	529	621
12 months or longer Fair Value	7,435	5,532
12 months or longer Unrealized Losses	564	535
Fixed maturities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	17,996	19,536
Total Unrealized Losses	1,053	1,099
Less than 12 months Fair Value	10,914	14,398
Less than 12 months Unrealized Losses	523	612
12 months or longer Fair Value	7,082	5,138
12 months or longer Unrealized Losses	530	487
Perpetual securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	340	479
Total Unrealized Losses	32	49
Less than 12 months Fair Value	0	85
Less than 12 months Unrealized Losses	0	1
12 months or longer Fair Value	340	394
12 months or longer Unrealized Losses	32	48
Equity securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	130	260
Total Unrealized Losses	8	8
Less than 12 months Fair Value	117	260
Less than 12 months Unrealized Losses	6	8
12 months or longer Fair Value	13	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	6,404	3,958
Total Unrealized Losses	423	160
Less than 12 months Fair Value	6,208	3,958
Less than 12 months Unrealized Losses	399	160
12 months or longer Fair Value	196	0
12 months or longer Unrealized Losses	24	0
Yen-denominated | Fixed maturities | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	152	105
Total Unrealized Losses	15	8
Less than 12 months Fair Value	62	105
Less than 12 months Unrealized Losses	3	8
12 months or longer Fair Value	90	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	95	635
Total Unrealized Losses	7	26
Less than 12 months Fair Value	69	347
Less than 12 months Unrealized Losses	6	14
12 months or longer Fair Value	26	288
12 months or longer Unrealized Losses	1	12
Yen-denominated | Fixed maturities | Sovereign and supranational
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	352	244
Total Unrealized Losses	3	13
Less than 12 months Fair Value	352	38
Less than 12 months Unrealized Losses	3	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	1,616	1,521
Total Unrealized Losses	77	100
Less than 12 months Fair Value	637	636
Less than 12 months Unrealized Losses	29	19
12 months or longer Fair Value	979	885
12 months or longer Unrealized Losses	48	81
Yen-denominated | Fixed maturities | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	424	321
Total Unrealized Losses	25	10
Less than 12 months Fair Value	386	321
Less than 12 months Unrealized Losses	24	10
12 months or longer Fair Value	38	0
12 months or longer Unrealized Losses	1	0
Yen-denominated | Perpetual securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	340	479
Total Unrealized Losses	32	49
Less than 12 months Fair Value	0	85
Less than 12 months Unrealized Losses	0	1
12 months or longer Fair Value	340	394
12 months or longer Unrealized Losses	32	48
Yen-denominated | Equity securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	72	49
Total Unrealized Losses	2	2
Less than 12 months Fair Value	67	49
Less than 12 months Unrealized Losses	1	2
12 months or longer Fair Value	5	0
12 months or longer Unrealized Losses	1	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	879	1,265
Total Unrealized Losses	34	60
Less than 12 months Fair Value	252	790
Less than 12 months Unrealized Losses	4	32
12 months or longer Fair Value	627	475
12 months or longer Unrealized Losses	30	28
Dollar-denominated | Fixed maturities | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	188	268
Total Unrealized Losses	7	16
Less than 12 months Fair Value	145	238
Less than 12 months Unrealized Losses	3	10
12 months or longer Fair Value	43	30
12 months or longer Unrealized Losses	4	6
Dollar-denominated | Fixed maturities | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	7,886	10,462
Total Unrealized Losses	462	690
Less than 12 months Fair Value	2,803	7,252
Less than 12 months Unrealized Losses	52	346
12 months or longer Fair Value	5,083	3,210
12 months or longer Unrealized Losses	410	344
Dollar-denominated | Equity securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	58	211
Total Unrealized Losses	6	6
Less than 12 months Fair Value	50	211
Less than 12 months Unrealized Losses	5	6
12 months or longer Fair Value	8	0
12 months or longer Unrealized Losses	$ 1	$ 0