INVESTMENTS - Investments in Debt Securities, Perpetual Securities and Equity Securities (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	$ 48,834	$ 47,009
Gross Unrealized Gains	968	992
Gross Unrealized Losses	1,358	1,618
Fair Value	48,444	46,383
Cost or Amortized Cost	49,680	52,275
Gross Unrealized Gains	3,557	3,679
Gross Unrealized Losses	1,338	1,918
Fair Value	51,899	54,036
Fixed Maturities
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	44,137	45,356
Gross Unrealized Gains	3,405	3,500
Gross Unrealized Losses	1,020	1,284
Fair Value	46,522	47,572
Fixed Maturities | Yen Denominated
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	48,834	47,009
Gross Unrealized Gains	968	992
Gross Unrealized Losses	1,358	1,618
Fair Value	48,444	46,383
Cost or Amortized Cost	26,559	28,099
Gross Unrealized Gains	1,142	1,053
Gross Unrealized Losses	886	1,061
Fair Value	26,815	28,091
Fixed Maturities | Yen Denominated | Japan government and agencies
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	22,783	18,775
Gross Unrealized Gains	287	297
Gross Unrealized Losses	3	1
Fair Value	23,067	19,071
Cost or Amortized Cost	10,007	11,108
Gross Unrealized Gains	604	670
Gross Unrealized Losses	0	0
Fair Value	10,611	11,778
Fixed Maturities | Yen Denominated | Municipalities
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	522	553
Gross Unrealized Gains	31	35
Gross Unrealized Losses	3	4
Fair Value	550	584
Fixed Maturities | Yen Denominated | Mortgage- and asset-backed Securities
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	117	129
Gross Unrealized Gains	4	5
Gross Unrealized Losses	0	0
Fair Value	121	134
Cost or Amortized Cost	846	912
Gross Unrealized Gains	37	43
Gross Unrealized Losses	1	1
Fair Value	882	954
Fixed Maturities | Yen Denominated | Public Utilities
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	5,189	5,615
Gross Unrealized Gains	175	188
Gross Unrealized Losses	157	166
Fair Value	5,207	5,637
Cost or Amortized Cost	3,933	3,850
Gross Unrealized Gains	65	59
Gross Unrealized Losses	220	226
Fair Value	3,778	3,683
Fixed Maturities | Yen Denominated | Sovereign and Supranational
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	3,970	4,200
Gross Unrealized Gains	149	148
Gross Unrealized Losses	166	183
Fair Value	3,953	4,165
Cost or Amortized Cost	1,612	1,704
Gross Unrealized Gains	69	87
Gross Unrealized Losses	19	16
Fair Value	1,662	1,775
Fixed Maturities | Yen Denominated | Banks/financial Institutions
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	11,559	12,389
Gross Unrealized Gains	174	170
Gross Unrealized Losses	855	1,079
Fair Value	10,878	11,480
Cost or Amortized Cost	4,163	4,312
Gross Unrealized Gains	202	74
Gross Unrealized Losses	287	359
Fair Value	4,078	4,027
Fixed Maturities | Yen Denominated | Other Corporate
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	4,694	5,348
Gross Unrealized Gains	148	149
Gross Unrealized Losses	174	185
Fair Value	4,668	5,312
Cost or Amortized Cost	5,998	6,213
Gross Unrealized Gains	165	120
Gross Unrealized Losses	359	459
Fair Value	5,804	5,874
Fixed Maturities | Dollar Denominated
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	17,578	17,257
Gross Unrealized Gains	2,263	2,447
Gross Unrealized Losses	134	223
Fair Value	19,707	19,481
Fixed Maturities | Dollar Denominated | U.S. Government and Agencies
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	100	31
Gross Unrealized Gains	18	4
Gross Unrealized Losses	0	0
Fair Value	118	35
Fixed Maturities | Dollar Denominated | Municipalities
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	1,061	1,060
Gross Unrealized Gains	110	107
Gross Unrealized Losses	8	8
Fair Value	1,163	1,159
Fixed Maturities | Dollar Denominated | Mortgage- and asset-backed Securities
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	307	310
Gross Unrealized Gains	75	74
Gross Unrealized Losses	0	0
Fair Value	382	384
Fixed Maturities | Dollar Denominated | Public Utilities
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	3,130	3,052
Gross Unrealized Gains	452	517
Gross Unrealized Losses	25	27
Fair Value	3,557	3,542
Fixed Maturities | Dollar Denominated | Sovereign and Supranational
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	454	449
Gross Unrealized Gains	93	89
Gross Unrealized Losses	4	5
Fair Value	543	533
Fixed Maturities | Dollar Denominated | Banks/financial Institutions
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	3,410	3,324
Gross Unrealized Gains	266	223
Gross Unrealized Losses	45	121
Fair Value	3,631	3,426
Fixed Maturities | Dollar Denominated | Other Corporate
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	9,116	9,031
Gross Unrealized Gains	1,249	1,433
Gross Unrealized Losses	52	62
Fair Value	10,313	10,402
Perpetual Securities
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	5,522	6,897
Gross Unrealized Gains	148	175
Gross Unrealized Losses	318	633
Fair Value	5,352	6,439
Perpetual Securities | Yen Denominated | Banks/financial Institutions
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	4,879	6,217
Gross Unrealized Gains	110	155
Gross Unrealized Losses	301	604
Fair Value	4,688	5,768
Perpetual Securities | Yen Denominated | Other Corporate
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	326	344
Gross Unrealized Gains	25	17
Gross Unrealized Losses	0	0
Fair Value	351	361
Perpetual Securities | Dollar Denominated | Banks/financial Institutions
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	317	336
Gross Unrealized Gains	13	3
Gross Unrealized Losses	17	29
Fair Value	313	310
Equity Securities
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	21	22
Gross Unrealized Gains	4	4
Gross Unrealized Losses	0	1
Fair Value	$ 25	$ 25