INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Detail) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	$ 18,645	$ 20,275
Total Unrealized Losses	1,174	1,156
Less than 12 months Fair Value	13,156	14,743
Less than 12 months Unrealized Losses	645	621
12 months or longer Fair Value	5,489	5,532
12 months or longer Unrealized Losses	529	535
Fixed maturities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	17,849	19,536
Total Unrealized Losses	1,124	1,099
Less than 12 months Fair Value	12,821	14,398
Less than 12 months Unrealized Losses	631	612
12 months or longer Fair Value	5,028	5,138
12 months or longer Unrealized Losses	493	487
Perpetual securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	429	479
Total Unrealized Losses	31	49
Less than 12 months Fair Value	0	85
Less than 12 months Unrealized Losses	0	1
12 months or longer Fair Value	429	394
12 months or longer Unrealized Losses	31	48
Equity securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	367	260
Total Unrealized Losses	19	8
Less than 12 months Fair Value	335	260
Less than 12 months Unrealized Losses	14	8
12 months or longer Fair Value	32	0
12 months or longer Unrealized Losses	5	0
Yen-denominated | Fixed maturities | Japan government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	6,241	3,958
Total Unrealized Losses	396	160
Less than 12 months Fair Value	6,234	3,958
Less than 12 months Unrealized Losses	395	160
12 months or longer Fair Value	7	0
12 months or longer Unrealized Losses	1	0
Yen-denominated | Fixed maturities | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	128	105
Total Unrealized Losses	14	8
Less than 12 months Fair Value	116	105
Less than 12 months Unrealized Losses	11	8
12 months or longer Fair Value	12	0
12 months or longer Unrealized Losses	3	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	96	635
Total Unrealized Losses	8	26
Less than 12 months Fair Value	96	347
Less than 12 months Unrealized Losses	8	14
12 months or longer Fair Value	0	288
12 months or longer Unrealized Losses	0	12
Yen-denominated | Fixed maturities | Sovereign and supranational
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	42	244
Total Unrealized Losses	3	13
Less than 12 months Fair Value	42	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	1,523	1,521
Total Unrealized Losses	79	100
Less than 12 months Fair Value	590	636
Less than 12 months Unrealized Losses	27	19
12 months or longer Fair Value	933	885
12 months or longer Unrealized Losses	52	81
Yen-denominated | Fixed maturities | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	169	321
Total Unrealized Losses	14	10
Less than 12 months Fair Value	132	321
Less than 12 months Unrealized Losses	13	10
12 months or longer Fair Value	37	0
12 months or longer Unrealized Losses	1	0
Yen-denominated | Perpetual securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	429	479
Total Unrealized Losses	31	49
Less than 12 months Fair Value	0	85
Less than 12 months Unrealized Losses	0	1
12 months or longer Fair Value	429	394
12 months or longer Unrealized Losses	31	48
Yen-denominated | Equity securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	99	49
Total Unrealized Losses	5	2
Less than 12 months Fair Value	80	49
Less than 12 months Unrealized Losses	3	2
12 months or longer Fair Value	19	0
12 months or longer Unrealized Losses	2	0
Dollar-denominated | Fixed maturities | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	45	44
Total Unrealized Losses	7	8
Less than 12 months Fair Value	0	0
Less than 12 months Unrealized Losses	0	0
12 months or longer Fair Value	45	44
12 months or longer Unrealized Losses	7	8
Dollar-denominated | Fixed maturities | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,121	1,265
Total Unrealized Losses	42	60
Less than 12 months Fair Value	623	790
Less than 12 months Unrealized Losses	14	32
12 months or longer Fair Value	498	475
12 months or longer Unrealized Losses	28	28
Dollar-denominated | Fixed maturities | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	232	268
Total Unrealized Losses	7	16
Less than 12 months Fair Value	216	238
Less than 12 months Unrealized Losses	5	10
12 months or longer Fair Value	16	30
12 months or longer Unrealized Losses	2	6
Dollar-denominated | Fixed maturities | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	8,252	10,462
Total Unrealized Losses	554	690
Less than 12 months Fair Value	4,772	7,252
Less than 12 months Unrealized Losses	155	346
12 months or longer Fair Value	3,480	3,210
12 months or longer Unrealized Losses	399	344
Dollar-denominated | Equity securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	268	211
Total Unrealized Losses	14	6
Less than 12 months Fair Value	255	211
Less than 12 months Unrealized Losses	11	6
12 months or longer Fair Value	13	0
12 months or longer Unrealized Losses	$ 3	$ 0