INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	$ 30,615	$ 29,310
Total Unrealized Losses	2,696	3,536
Less than 12 months Fair Value	11,157	10,115
Less than 12 months Unrealized Losses	321	523
12 months or longer Fair Value	19,458	19,195
12 months or longer Unrealized Losses	2,375	3,013
Banks/financial Institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	12,000
Total Unrealized Losses	1,500
Fixed Maturities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	28,459	26,795
Total Unrealized Losses	2,378	2,902
Less than 12 months Fair Value	10,476	9,370
Less than 12 months Unrealized Losses	279	449
12 months or longer Fair Value	17,983	17,425
12 months or longer Unrealized Losses	2,099	2,453
Fixed Maturities | Japan government and agencies | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	3,674	940
Total Unrealized Losses	3	1
Less than 12 months Fair Value	3,597	859
Less than 12 months Unrealized Losses	2	1
12 months or longer Fair Value	77	81
12 months or longer Unrealized Losses	1	0
Fixed Maturities | Municipalities | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	60	54
Total Unrealized Losses	8	8
Less than 12 months Fair Value	29	22
Less than 12 months Unrealized Losses	1	1
12 months or longer Fair Value	31	32
12 months or longer Unrealized Losses	7	7
Fixed Maturities | Municipalities | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	58	60
Total Unrealized Losses	3	4
Less than 12 months Fair Value	0	0
Less than 12 months Unrealized Losses	0	0
12 months or longer Fair Value	58	60
12 months or longer Unrealized Losses	3	4
Fixed Maturities | Mortgage- and asset-backed Securities | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	143	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	143	151
12 months or longer Unrealized Losses	1	1
Fixed Maturities | Public Utilities | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	439	295
Total Unrealized Losses	25	27
Less than 12 months Fair Value	284	110
Less than 12 months Unrealized Losses	11	3
12 months or longer Fair Value	155	185
12 months or longer Unrealized Losses	14	24
Fixed Maturities | Public Utilities | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	4,779	4,995
Total Unrealized Losses	377	392
Less than 12 months Fair Value	2,094	2,404
Less than 12 months Unrealized Losses	131	141
12 months or longer Fair Value	2,685	2,591
12 months or longer Unrealized Losses	246	251
Fixed Maturities | Sovereign and Supranational | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	68	66
Total Unrealized Losses	4	5
Less than 12 months Fair Value	17	34
Less than 12 months Unrealized Losses	0	2
12 months or longer Fair Value	51	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	2,589	2,349
Total Unrealized Losses	185	199
Less than 12 months Fair Value	592	749
Less than 12 months Unrealized Losses	17	62
12 months or longer Fair Value	1,997	1,600
12 months or longer Unrealized Losses	168	137
Fixed Maturities | Banks/financial Institutions | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	593	770
Total Unrealized Losses	45	121
Less than 12 months Fair Value	219	391
Less than 12 months Unrealized Losses	9	56
12 months or longer Fair Value	374	379
12 months or longer Unrealized Losses	36	65
Fixed Maturities | Banks/financial Institutions | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	9,247	10,175
Total Unrealized Losses	1,142	1,438
Less than 12 months Fair Value	926	1,639
Less than 12 months Unrealized Losses	11	46
12 months or longer Fair Value	8,321	8,536
12 months or longer Unrealized Losses	1,131	1,392
Fixed Maturities | Other Corporate | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,286	834
Total Unrealized Losses	52	62
Less than 12 months Fair Value	1,112	639
Less than 12 months Unrealized Losses	28	27
12 months or longer Fair Value	174	195
12 months or longer Unrealized Losses	24	35
Fixed Maturities | Other Corporate | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	5,523	6,106
Total Unrealized Losses	533	644
Less than 12 months Fair Value	1,606	2,523
Less than 12 months Unrealized Losses	69	110
12 months or longer Fair Value	3,917	3,583
12 months or longer Unrealized Losses	464	534
Perpetual Securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	2,152	2,507
Total Unrealized Losses	318	633
Less than 12 months Fair Value	679	739
Less than 12 months Unrealized Losses	42	73
12 months or longer Fair Value	1,473	1,768
12 months or longer Unrealized Losses	276	560
Perpetual Securities | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	116	217
Total Unrealized Losses	17	29
Less than 12 months Fair Value	60	109
Less than 12 months Unrealized Losses	0	4
12 months or longer Fair Value	56	108
12 months or longer Unrealized Losses	17	25
Perpetual Securities | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	2,036	2,290
Total Unrealized Losses	301	604
Less than 12 months Fair Value	619	630
Less than 12 months Unrealized Losses	42	69
12 months or longer Fair Value	1,417	1,660
12 months or longer Unrealized Losses	259	535
Equity Securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	4	8
Total Unrealized Losses	0	1
Less than 12 months Fair Value	2	6
Less than 12 months Unrealized Losses	0	1
12 months or longer Fair Value	2	2
12 months or longer Unrealized Losses	$ 0	$ 0