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, 2017	Dec. 31, 2016
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	$ 21,897	$ 20,275
Total Unrealized Losses	1,415	1,156
Less than 12 months Fair Value	16,067	14,743
Less than 12 months Unrealized Losses	768	621
12 months or longer Fair Value	5,830	5,532
12 months or longer Unrealized Losses	647	535
Fixed maturities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	21,149	19,536
Total Unrealized Losses	1,344	1,099
Less than 12 months Fair Value	15,778	14,398
Less than 12 months Unrealized Losses	755	612
12 months or longer Fair Value	5,371	5,138
12 months or longer Unrealized Losses	589	487
Perpetual securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	409	479
Total Unrealized Losses	50	49
Less than 12 months Fair Value	0	85
Less than 12 months Unrealized Losses	0	1
12 months or longer Fair Value	409	394
12 months or longer Unrealized Losses	50	48
Equity securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	339	260
Total Unrealized Losses	21	8
Less than 12 months Fair Value	289	260
Less than 12 months Unrealized Losses	13	8
12 months or longer Fair Value	50	0
12 months or longer Unrealized Losses	8	0
Yen-denominated | Fixed maturities | Japan government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	5,940	3,958
Total Unrealized Losses	366	160
Less than 12 months Fair Value	5,940	3,958
Less than 12 months Unrealized Losses	366	160
12 months or longer Fair Value	0	0
12 months or longer Unrealized Losses	0	0
Yen-denominated | Fixed maturities | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	132	105
Total Unrealized Losses	12	8
Less than 12 months Fair Value	132	105
Less than 12 months Unrealized Losses	12	8
12 months or longer Fair Value	0	0
12 months or longer Unrealized Losses	0	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	325	635
Total Unrealized Losses	13	26
Less than 12 months Fair Value	127	347
Less than 12 months Unrealized Losses	6	14
12 months or longer Fair Value	198	288
12 months or longer Unrealized Losses	7	12
Yen-denominated | Fixed maturities | Sovereign and supranational
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	39	244
Total Unrealized Losses	6	13
Less than 12 months Fair Value	39	38
Less than 12 months Unrealized Losses	6	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	1,531	1,521
Total Unrealized Losses	107	100
Less than 12 months Fair Value	646	636
Less than 12 months Unrealized Losses	34	19
12 months or longer Fair Value	885	885
12 months or longer Unrealized Losses	73	81
Yen-denominated | Fixed maturities | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	415	321
Total Unrealized Losses	16	10
Less than 12 months Fair Value	415	321
Less than 12 months Unrealized Losses	16	10
12 months or longer Fair Value	0	0
12 months or longer Unrealized Losses	0	0
Yen-denominated | Perpetual securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	409	479
Total Unrealized Losses	50	49
Less than 12 months Fair Value	0	85
Less than 12 months Unrealized Losses	0	1
12 months or longer Fair Value	409	394
12 months or longer Unrealized Losses	50	48
Yen-denominated | Equity securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	208	49
Total Unrealized Losses	10	2
Less than 12 months Fair Value	172	49
Less than 12 months Unrealized Losses	5	2
12 months or longer Fair Value	36	0
12 months or longer Unrealized Losses	5	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	1,642	1,265
Total Unrealized Losses	77	60
Less than 12 months Fair Value	1,124	790
Less than 12 months Unrealized Losses	37	32
12 months or longer Fair Value	518	475
12 months or longer Unrealized Losses	40	28
Dollar-denominated | Fixed maturities | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	390	268
Total Unrealized Losses	18	16
Less than 12 months Fair Value	309	238
Less than 12 months Unrealized Losses	6	10
12 months or longer Fair Value	81	30
12 months or longer Unrealized Losses	12	6
Dollar-denominated | Fixed maturities | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	10,690	10,462
Total Unrealized Losses	722	690
Less than 12 months Fair Value	7,046	7,252
Less than 12 months Unrealized Losses	272	346
12 months or longer Fair Value	3,644	3,210
12 months or longer Unrealized Losses	450	344
Dollar-denominated | Equity securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	131	211
Total Unrealized Losses	11	6
Less than 12 months Fair Value	117	211
Less than 12 months Unrealized Losses	8	6
12 months or longer Fair Value	14	0
12 months or longer Unrealized Losses	$ 3	$ 0