INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	$ 40,707	$ 29,310
Total Unrealized Losses	1,582	3,536
Less Than 12 months Fair Value	28,268	10,115
Less Than 12 months Unrealized Losses	368	523
12 months or longer Fair Value	12,439	19,195
12 months or longer Unrealized Losses	1,214	3,013
Banks/financial Institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	8,600
Total Unrealized Losses	787
Fixed Maturities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	39,250	26,795
Total Unrealized Losses	1,411	2,902
Less Than 12 months Fair Value	28,145	9,370
Less Than 12 months Unrealized Losses	368	449
12 months or longer Fair Value	11,105	17,425
12 months or longer Unrealized Losses	1,043	2,453
Fixed Maturities | Japan government and agencies | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	17,342	940
Total Unrealized Losses	148	1
Less Than 12 months Fair Value	17,342	859
Less Than 12 months Unrealized Losses	148	1
12 months or longer Fair Value	0	81
12 months or longer Unrealized Losses	0	0
Fixed Maturities | Municipalities | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	34	54
Total Unrealized Losses	6	8
Less Than 12 months Fair Value	1	22
Less Than 12 months Unrealized Losses	0	1
12 months or longer Fair Value	33	32
12 months or longer Unrealized Losses	6	7
Fixed Maturities | Municipalities | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	56	60
Total Unrealized Losses	2	4
Less Than 12 months Fair Value	56	0
Less Than 12 months Unrealized Losses	2	0
12 months or longer Fair Value	0	60
12 months or longer Unrealized Losses	0	4
Fixed Maturities | Mortgage- and asset-backed Securities | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	10
Total Unrealized Losses	0
Less Than 12 months Fair Value	10
Less Than 12 months Unrealized Losses	0
12 months or longer Fair Value	0
12 months or longer Unrealized Losses	0
Fixed Maturities | Mortgage- and asset-backed Securities | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	136	151
Total Unrealized Losses	1	1
Less Than 12 months Fair Value	0	0
Less Than 12 months Unrealized Losses	0	0
12 months or longer Fair Value	136	151
12 months or longer Unrealized Losses	1	1
Fixed Maturities | Public Utilities | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	736	295
Total Unrealized Losses	17	27
Less Than 12 months Fair Value	736	110
Less Than 12 months Unrealized Losses	17	3
12 months or longer Fair Value	0	185
12 months or longer Unrealized Losses	0	24
Fixed Maturities | Public Utilities | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	3,920	4,995
Total Unrealized Losses	178	392
Less Than 12 months Fair Value	1,339	2,404
Less Than 12 months Unrealized Losses	31	141
12 months or longer Fair Value	2,581	2,591
12 months or longer Unrealized Losses	147	251
Fixed Maturities | Sovereign and Supranational | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	31	66
Total Unrealized Losses	2	5
Less Than 12 months Fair Value	0	34
Less Than 12 months Unrealized Losses	0	2
12 months or longer Fair Value	31	32
12 months or longer Unrealized Losses	2	3
Fixed Maturities | Sovereign and Supranational | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,244	2,349
Total Unrealized Losses	84	199
Less Than 12 months Fair Value	507	749
Less Than 12 months Unrealized Losses	13	62
12 months or longer Fair Value	737	1,600
12 months or longer Unrealized Losses	71	137
Fixed Maturities | Banks/financial Institutions | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	276	770
Total Unrealized Losses	6	121
Less Than 12 months Fair Value	180	391
Less Than 12 months Unrealized Losses	3	56
12 months or longer Fair Value	96	379
12 months or longer Unrealized Losses	3	65
Fixed Maturities | Banks/financial Institutions | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	6,918	10,175
Total Unrealized Losses	611	1,438
Less Than 12 months Fair Value	1,935	1,639
Less Than 12 months Unrealized Losses	28	46
12 months or longer Fair Value	4,983	8,536
12 months or longer Unrealized Losses	583	1,392
Fixed Maturities | Other Corporate | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	4,534	834
Total Unrealized Losses	95	62
Less Than 12 months Fair Value	4,404	639
Less Than 12 months Unrealized Losses	86	27
12 months or longer Fair Value	130	195
12 months or longer Unrealized Losses	9	35
Fixed Maturities | Other Corporate | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	4,013	6,106
Total Unrealized Losses	261	644
Less Than 12 months Fair Value	1,635	2,523
Less Than 12 months Unrealized Losses	40	110
12 months or longer Fair Value	2,378	3,583
12 months or longer Unrealized Losses	221	534
Perpetual securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,451	2,507
Total Unrealized Losses	170	633
Less Than 12 months Fair Value	120	739
Less Than 12 months Unrealized Losses	0	73
12 months or longer Fair Value	1,331	1,768
12 months or longer Unrealized Losses	170	560
Perpetual securities | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	136	217
Total Unrealized Losses	9	29
Less Than 12 months Fair Value	120	109
Less Than 12 months Unrealized Losses	0	4
12 months or longer Fair Value	16	108
12 months or longer Unrealized Losses	9	25
Perpetual securities | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,315	2,290
Total Unrealized Losses	161	604
Less Than 12 months Fair Value	0	630
Less Than 12 months Unrealized Losses	0	69
12 months or longer Fair Value	1,315	1,660
12 months or longer Unrealized Losses	161	535
Equity securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	6	8
Total Unrealized Losses	1	1
Less Than 12 months Fair Value	3	6
Less Than 12 months Unrealized Losses	0	1
12 months or longer Fair Value	3	2
12 months or longer Unrealized Losses	$ 1	$ 0