INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	$ 28,450	$ 29,310
Total Unrealized Losses	1,874	3,536
Less than 12 months Fair Value	11,860	10,115
Less than 12 months Unrealized Losses	184	523
12 months or longer Fair Value	16,590	19,195
12 months or longer Unrealized Losses	1,690	3,013
Banks/financial Institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	8,600
Total Unrealized Losses	1,100
Fixed Maturities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	26,558	26,795
Total Unrealized Losses	1,579	2,902
Less than 12 months Fair Value	11,611	9,370
Less than 12 months Unrealized Losses	179	449
12 months or longer Fair Value	14,947	17,425
12 months or longer Unrealized Losses	1,400	2,453
Fixed Maturities | Japan government and agencies | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	7,617	940
Total Unrealized Losses	12	1
Less than 12 months Fair Value	7,617	859
Less than 12 months Unrealized Losses	12	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	33	54
Total Unrealized Losses	5	8
Less than 12 months Fair Value	0	22
Less than 12 months Unrealized Losses	0	1
12 months or longer Fair Value	33	32
12 months or longer Unrealized Losses	5	7
Fixed Maturities | Municipalities | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		60
Total Unrealized Losses		4
Less than 12 months Fair Value		0
Less than 12 months Unrealized Losses		0
12 months or longer Fair Value		60
12 months or longer Unrealized Losses		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	152	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	152	151
12 months or longer Unrealized Losses	1	1
Fixed Maturities | Public Utilities | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	185	295
Total Unrealized Losses	3	27
Less than 12 months Fair Value	145	110
Less than 12 months Unrealized Losses	2	3
12 months or longer Fair Value	40	185
12 months or longer Unrealized Losses	1	24
Fixed Maturities | Public Utilities | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	4,030	4,995
Total Unrealized Losses	208	392
Less than 12 months Fair Value	642	2,404
Less than 12 months Unrealized Losses	24	141
12 months or longer Fair Value	3,388	2,591
12 months or longer Unrealized Losses	184	251
Fixed Maturities | Sovereign and Supranational | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	37	66
Total Unrealized Losses	4	5
Less than 12 months Fair Value	6	34
Less than 12 months Unrealized Losses	0	2
12 months or longer Fair Value	31	32
12 months or longer Unrealized Losses	4	3
Fixed Maturities | Sovereign and Supranational | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,796	2,349
Total Unrealized Losses	188	199
Less than 12 months Fair Value	913	749
Less than 12 months Unrealized Losses	104	62
12 months or longer Fair Value	883	1,600
12 months or longer Unrealized Losses	84	137
Fixed Maturities | Banks/financial Institutions | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	304	770
Total Unrealized Losses	17	121
Less than 12 months Fair Value	99	391
Less than 12 months Unrealized Losses	1	56
12 months or longer Fair Value	205	379
12 months or longer Unrealized Losses	16	65
Fixed Maturities | Banks/financial Institutions | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	6,408	10,175
Total Unrealized Losses	768	1,438
Less than 12 months Fair Value	189	1,639
Less than 12 months Unrealized Losses	5	46
12 months or longer Fair Value	6,219	8,536
12 months or longer Unrealized Losses	763	1,392
Fixed Maturities | Other Corporate | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,334	834
Total Unrealized Losses	39	62
Less than 12 months Fair Value	1,225	639
Less than 12 months Unrealized Losses	24	27
12 months or longer Fair Value	109	195
12 months or longer Unrealized Losses	15	35
Fixed Maturities | Other Corporate | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	4,652	6,106
Total Unrealized Losses	334	644
Less than 12 months Fair Value	765	2,523
Less than 12 months Unrealized Losses	7	110
12 months or longer Fair Value	3,887	3,583
12 months or longer Unrealized Losses	327	534
Perpetual Securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,884	2,507
Total Unrealized Losses	293	633
Less than 12 months Fair Value	244	739
Less than 12 months Unrealized Losses	4	73
12 months or longer Fair Value	1,640	1,768
12 months or longer Unrealized Losses	289	560
Perpetual Securities | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	133	217
Total Unrealized Losses	12	29
Less than 12 months Fair Value	118	109
Less than 12 months Unrealized Losses	2	4
12 months or longer Fair Value	15	108
12 months or longer Unrealized Losses	10	25
Perpetual Securities | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,751	2,290
Total Unrealized Losses	281	604
Less than 12 months Fair Value	126	630
Less than 12 months Unrealized Losses	2	69
12 months or longer Fair Value	1,625	1,660
12 months or longer Unrealized Losses	279	535
Equity Securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	8	8
Total Unrealized Losses	2	1
Less than 12 months Fair Value	5	6
Less than 12 months Unrealized Losses	1	1
12 months or longer Fair Value	3	2
12 months or longer Unrealized Losses	$ 1	$ 0