INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	$ 26,627	$ 29,310
Total Unrealized Losses	3,057	3,536
Less than 12 months Fair Value	8,343	10,115
Less than 12 months Unrealized Losses	440	523
12 months or longer Fair Value	18,284	19,195
12 months or longer Unrealized Losses	2,617	3,013
Banks/financial Institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	11,500
Total Unrealized Losses	1,900
Fixed Maturities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	24,142	26,795
Total Unrealized Losses	2,467	2,902
Less than 12 months Fair Value	7,285	9,370
Less than 12 months Unrealized Losses	322	449
12 months or longer Fair Value	16,857	17,425
12 months or longer Unrealized Losses	2,145	2,453
Fixed Maturities | Japan government and agencies | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,397	940
Total Unrealized Losses	6	1
Less than 12 months Fair Value	1,397	859
Less than 12 months Unrealized Losses	6	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	51	54
Total Unrealized Losses	7	8
Less than 12 months Fair Value	19	22
Less than 12 months Unrealized Losses	0	1
12 months or longer Fair Value	32	32
12 months or longer Unrealized Losses	7	7
Fixed Maturities | Municipalities | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	61	60
Total Unrealized Losses	2	4
Less than 12 months Fair Value	0	0
Less than 12 months Unrealized Losses	0	0
12 months or longer Fair Value	61	60
12 months or longer Unrealized Losses	2	4
Fixed Maturities | Mortgage- and asset-backed Securities | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	10
Total Unrealized Losses	1
Less than 12 months Fair Value	10
Less than 12 months Unrealized Losses	1
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	149	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	149	151
12 months or longer Unrealized Losses	1	1
Fixed Maturities | Public Utilities | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	347	295
Total Unrealized Losses	28	27
Less than 12 months Fair Value	210	110
Less than 12 months Unrealized Losses	14	3
12 months or longer Fair Value	137	185
12 months or longer Unrealized Losses	14	24
Fixed Maturities | Public Utilities | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	4,810	4,995
Total Unrealized Losses	398	392
Less than 12 months Fair Value	1,822	2,404
Less than 12 months Unrealized Losses	141	141
12 months or longer Fair Value	2,988	2,591
12 months or longer Unrealized Losses	257	251
Fixed Maturities | Sovereign and Supranational | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	57	66
Total Unrealized Losses	3	5
Less than 12 months Fair Value	6	34
Less than 12 months Unrealized Losses	0	2
12 months or longer Fair Value	51	32
12 months or longer Unrealized Losses	3	3
Fixed Maturities | Sovereign and Supranational | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	2,355	2,349
Total Unrealized Losses	167	199
Less than 12 months Fair Value	757	749
Less than 12 months Unrealized Losses	63	62
12 months or longer Fair Value	1,598	1,600
12 months or longer Unrealized Losses	104	137
Fixed Maturities | Banks/financial Institutions | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	543	770
Total Unrealized Losses	41	121
Less than 12 months Fair Value	230	391
Less than 12 months Unrealized Losses	6	56
12 months or longer Fair Value	313	379
12 months or longer Unrealized Losses	35	65
Fixed Maturities | Banks/financial Institutions | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	8,450	10,175
Total Unrealized Losses	1,245	1,438
Less than 12 months Fair Value	1,263	1,639
Less than 12 months Unrealized Losses	23	46
12 months or longer Fair Value	7,187	8,536
12 months or longer Unrealized Losses	1,222	1,392
Fixed Maturities | Other Corporate | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	680	834
Total Unrealized Losses	39	62
Less than 12 months Fair Value	530	639
Less than 12 months Unrealized Losses	13	27
12 months or longer Fair Value	150	195
12 months or longer Unrealized Losses	26	35
Fixed Maturities | Other Corporate | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	5,232	6,106
Total Unrealized Losses	529	644
Less than 12 months Fair Value	1,041	2,523
Less than 12 months Unrealized Losses	55	110
12 months or longer Fair Value	4,191	3,583
12 months or longer Unrealized Losses	474	534
Perpetual Securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	2,475	2,507
Total Unrealized Losses	588	633
Less than 12 months Fair Value	1,050	739
Less than 12 months Unrealized Losses	117	73
12 months or longer Fair Value	1,425	1,768
12 months or longer Unrealized Losses	471	560
Perpetual Securities | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	126	217
Total Unrealized Losses	18	29
Less than 12 months Fair Value	111	109
Less than 12 months Unrealized Losses	9	4
12 months or longer Fair Value	15	108
12 months or longer Unrealized Losses	9	25
Perpetual Securities | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	2,349	2,290
Total Unrealized Losses	570	604
Less than 12 months Fair Value	939	630
Less than 12 months Unrealized Losses	108	69
12 months or longer Fair Value	1,410	1,660
12 months or longer Unrealized Losses	462	535
Equity Securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	10	8
Total Unrealized Losses	2	1
Less than 12 months Fair Value	8	6
Less than 12 months Unrealized Losses	1	1
12 months or longer Fair Value	2	2
12 months or longer Unrealized Losses	$ 1	$ 0