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, 2016	Dec. 31, 2015
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	$ 14,712	$ 22,413
Total Unrealized Losses	1,149	2,013
Less than 12 months Fair Value	7,418	16,529
Less than 12 months Unrealized Losses	353	1,040
12 months or longer Fair Value	7,294	5,884
12 months or longer Unrealized Losses	796	973
Fixed maturities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	13,517	21,571
Total Unrealized Losses	972	1,915
Less than 12 months Fair Value	6,756	16,122
Less than 12 months Unrealized Losses	301	1,024
12 months or longer Fair Value	6,761	5,449
12 months or longer Unrealized Losses	671	891
Perpetual securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	630	651
Total Unrealized Losses	126	94
Less than 12 months Fair Value	97	216
Less than 12 months Unrealized Losses	1	12
12 months or longer Fair Value	533	435
12 months or longer Unrealized Losses	125	82
Equity securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	565	191
Total Unrealized Losses	51	4
Less than 12 months Fair Value	565	191
Less than 12 months Unrealized Losses	51	4
12 months or longer Fair Value	0	0
12 months or longer Unrealized Losses	0	0
Yen-denominated | Fixed maturities | Japan government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	689
Total Unrealized Losses	23
Less than 12 months Fair Value	689
Less than 12 months Unrealized Losses	23
12 months or longer Fair Value	0
12 months or longer Unrealized Losses	0
Yen-denominated | Fixed maturities | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	62
Total Unrealized Losses	2
Less than 12 months Fair Value	62
Less than 12 months Unrealized Losses	2
12 months or longer Fair Value	0
12 months or longer Unrealized Losses	0
Yen-denominated | Fixed maturities | Mortgage- and asset-backed securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	413
Total Unrealized Losses	3
Less than 12 months Fair Value	413
Less than 12 months Unrealized Losses	3
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	648	1,487
Total Unrealized Losses	14	104
Less than 12 months Fair Value	313	1,062
Less than 12 months Unrealized Losses	3	73
12 months or longer Fair Value	335	425
12 months or longer Unrealized Losses	11	31
Yen-denominated | Fixed maturities | Sovereign and supranational
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	242	580
Total Unrealized Losses	6	26
Less than 12 months Fair Value	0	385
Less than 12 months Unrealized Losses	0	13
12 months or longer Fair Value	242	195
12 months or longer Unrealized Losses	6	13
Yen-denominated | Fixed maturities | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,415	2,350
Total Unrealized Losses	124	158
Less than 12 months Fair Value	324	1,147
Less than 12 months Unrealized Losses	4	14
12 months or longer Fair Value	1,091	1,203
12 months or longer Unrealized Losses	120	144
Yen-denominated | Fixed maturities | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	897	1,151
Total Unrealized Losses	53	77
Less than 12 months Fair Value	364	343
Less than 12 months Unrealized Losses	13	5
12 months or longer Fair Value	533	808
12 months or longer Unrealized Losses	40	72
Yen-denominated | Perpetual securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	630	645
Total Unrealized Losses	126	93
Less than 12 months Fair Value	97	216
Less than 12 months Unrealized Losses	1	12
12 months or longer Fair Value	533	429
12 months or longer Unrealized Losses	125	81
Yen-denominated | Equity securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	382	191
Total Unrealized Losses	42	4
Less than 12 months Fair Value	382	191
Less than 12 months Unrealized Losses	42	4
12 months or longer Fair Value	0	0
12 months or longer Unrealized Losses	0	0
Dollar-denominated | Fixed maturities | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	50	80
Total Unrealized Losses	3	6
Less than 12 months Fair Value	0	80
Less than 12 months Unrealized Losses	0	6
12 months or longer Fair Value	50	0
12 months or longer Unrealized Losses	3	0
Dollar-denominated | Fixed maturities | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,199	2,127
Total Unrealized Losses	54	221
Less than 12 months Fair Value	448	1,689
Less than 12 months Unrealized Losses	13	132
12 months or longer Fair Value	751	438
12 months or longer Unrealized Losses	41	89
Dollar-denominated | Fixed maturities | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	150	366
Total Unrealized Losses	11	21
Less than 12 months Fair Value	85	348
Less than 12 months Unrealized Losses	4	11
12 months or longer Fair Value	65	18
12 months or longer Unrealized Losses	7	10
Dollar-denominated | Fixed maturities | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	7,752	13,430
Total Unrealized Losses	679	1,302
Less than 12 months Fair Value	4,058	11,068
Less than 12 months Unrealized Losses	236	770
12 months or longer Fair Value	3,694	2,362
12 months or longer Unrealized Losses	443	532
Dollar-denominated | Perpetual securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		6
Total Unrealized Losses		1
Less than 12 months Fair Value		0
Less than 12 months Unrealized Losses		0
12 months or longer Fair Value		6
12 months or longer Unrealized Losses		$ 1
Dollar-denominated | Equity securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	183
Total Unrealized Losses	9
Less than 12 months Fair Value	183
Less than 12 months Unrealized Losses	9
12 months or longer Fair Value	0
12 months or longer Unrealized Losses	$ 0