Fair Value and Gross Unrealized Losses for Securities That Have Been in a Continuous Unrealized Loss Position (Detail) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	$ 29,906	$ 30,654
Total Unrealized Losses	2,530	3,363
Less than 12 months Fair Value	10,451	10,582
Less than 12 months Unrealized Losses	278	435
12 months or longer Fair Value	19,455	20,072
12 months or longer Unrealized Losses	2,252	2,928
Fixed Maturities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	26,592	26,262
Total Unrealized Losses	2,131	2,798
Less than 12 months Fair Value	9,846	8,627
Less than 12 months Unrealized Losses	253	296
12 months or longer Fair Value	16,746	17,635
12 months or longer Unrealized Losses	1,878	2,502
Fixed Maturities | Yen Denominated | Japan government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,590	1,634
Total Unrealized Losses	16	18
Less than 12 months Fair Value	1,590	1,634
Less than 12 months Unrealized Losses	16	18
12 months or longer Fair Value	0	0
12 months or longer Unrealized Losses	0	0
Fixed Maturities | Yen Denominated | Mortgage- and asset-backed Securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	154	415
Total Unrealized Losses	5	15
Less than 12 months Fair Value	12	415
Less than 12 months Unrealized Losses	1	15
12 months or longer Fair Value	142	0
12 months or longer Unrealized Losses	4	0
Fixed Maturities | Yen Denominated | Public Utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	4,340	2,877
Total Unrealized Losses	244	200
Less than 12 months Fair Value	1,886	766
Less than 12 months Unrealized Losses	42	47
12 months or longer Fair Value	2,454	2,111
12 months or longer Unrealized Losses	202	153
Fixed Maturities | Yen Denominated | Sovereign and Supranational
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	2,115	1,579
Total Unrealized Losses	108	77
Less than 12 months Fair Value	968	428
Less than 12 months Unrealized Losses	16	1
12 months or longer Fair Value	1,147	1,151
12 months or longer Unrealized Losses	92	76
Fixed Maturities | Yen Denominated | Banks/financial Institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	9,517	10,609
Total Unrealized Losses	999	1,703
Less than 12 months Fair Value	1,111	1,506
Less than 12 months Unrealized Losses	29	40
12 months or longer Fair Value	8,406	9,103
12 months or longer Unrealized Losses	970	1,663
Fixed Maturities | Yen Denominated | Other Corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	4,739	4,503
Total Unrealized Losses	574	503
Less than 12 months Fair Value	1,248	507
Less than 12 months Unrealized Losses	53	45
12 months or longer Fair Value	3,491	3,996
12 months or longer Unrealized Losses	521	458
Fixed Maturities | Yen Denominated | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	58	59
Total Unrealized Losses	4	2
Less than 12 months Fair Value	0	0
Less than 12 months Unrealized Losses	0	0
12 months or longer Fair Value	58	59
12 months or longer Unrealized Losses	4	2
Fixed Maturities | Dollar Denominated | Mortgage- and asset-backed Securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	20	78
Total Unrealized Losses	1	13
Less than 12 months Fair Value	5	20
Less than 12 months Unrealized Losses	0	0
12 months or longer Fair Value	15	58
12 months or longer Unrealized Losses	1	13
Fixed Maturities | Dollar Denominated | Public Utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	636	556
Total Unrealized Losses	35	36
Less than 12 months Fair Value	585	498
Less than 12 months Unrealized Losses	28	28
12 months or longer Fair Value	51	58
12 months or longer Unrealized Losses	7	8
Fixed Maturities | Dollar Denominated | Sovereign and Supranational
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	62	45
Total Unrealized Losses	3	2
Less than 12 months Fair Value	29	12
Less than 12 months Unrealized Losses	1	0
12 months or longer Fair Value	33	33
12 months or longer Unrealized Losses	2	2
Fixed Maturities | Dollar Denominated | Banks/financial Institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,074	1,484
Total Unrealized Losses	52	108
Less than 12 months Fair Value	535	753
Less than 12 months Unrealized Losses	15	22
12 months or longer Fair Value	539	731
12 months or longer Unrealized Losses	37	86
Fixed Maturities | Dollar Denominated | Other Corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,882	1,741
Total Unrealized Losses	69	79
Less than 12 months Fair Value	1,512	1,456
Less than 12 months Unrealized Losses	43	52
12 months or longer Fair Value	370	285
12 months or longer Unrealized Losses	26	27
Fixed Maturities | Dollar Denominated | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	405	682
Total Unrealized Losses	21	42
Less than 12 months Fair Value	365	632
Less than 12 months Unrealized Losses	9	28
12 months or longer Fair Value	40	50
12 months or longer Unrealized Losses	12	14
Perpetual Securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	3,306	4,379
Total Unrealized Losses	397	563
Less than 12 months Fair Value	599	1,942
Less than 12 months Unrealized Losses	24	138
12 months or longer Fair Value	2,707	2,437
12 months or longer Unrealized Losses	373	425
Perpetual Securities | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	3,096	4,171
Total Unrealized Losses	374	533
Less than 12 months Fair Value	482	1,793
Less than 12 months Unrealized Losses	21	119
12 months or longer Fair Value	2,614	2,378
12 months or longer Unrealized Losses	353	414
Perpetual Securities | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	210	208
Total Unrealized Losses	23	30
Less than 12 months Fair Value	117	149
Less than 12 months Unrealized Losses	3	19
12 months or longer Fair Value	93	59
12 months or longer Unrealized Losses	20	11
Equity Securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	8	13
Total Unrealized Losses	2	2
Less than 12 months Fair Value	6	13
Less than 12 months Unrealized Losses	1	1
12 months or longer Fair Value	2	0
12 months or longer Unrealized Losses	1	1
Banks/financial Institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	13,900
Total Unrealized Losses	$ 1,400