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, 2013	Dec. 31, 2012
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	$ 26,588	$ 40,707
Total Unrealized Losses	2,683	1,582
Less than 12 months Fair Value	19,156	28,268
Less than 12 months Unrealized Losses	1,199	368
12 months or longer Fair Value	7,432	12,439
12 months or longer Unrealized Losses	1,484	1,214
Banks/financial Institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	8,700
Total Unrealized Losses	1,500
Fixed Maturities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	24,524	39,250
Total Unrealized Losses	2,085	1,411
Less than 12 months Fair Value	17,807	28,145
Less than 12 months Unrealized Losses	874	368
12 months or longer Fair Value	6,717	11,105
12 months or longer Unrealized Losses	1,211	1,043
Fixed Maturities | Japan government and agencies | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	5	17,342
Total Unrealized Losses	0	148
Less than 12 months Fair Value	5	17,342
Less than 12 months Unrealized Losses	0	148
12 months or longer Fair Value	0	0
12 months or longer Unrealized Losses	0	0
Fixed Maturities | Municipalities | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	34	34
Total Unrealized Losses	6	6
Less than 12 months Fair Value	0	1
Less than 12 months Unrealized Losses	0	0
12 months or longer Fair Value	34	33
12 months or longer Unrealized Losses	6	6
Fixed Maturities | Municipalities | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		56
Total Unrealized Losses		2
Less than 12 months Fair Value		56
Less than 12 months Unrealized Losses		2
12 months or longer Fair Value		0
12 months or longer Unrealized Losses		0
Fixed Maturities | Mortgage- and asset-backed Securities | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	9	10
Total Unrealized Losses	0	0
Less than 12 months Fair Value	9	10
Less than 12 months Unrealized Losses	0	0
12 months or longer Fair Value	0	0
12 months or longer Unrealized Losses	0	0
Fixed Maturities | Mortgage- and asset-backed Securities | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	125	136
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	125	136
12 months or longer Unrealized Losses	1	1
Fixed Maturities | Public Utilities | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1,154	736
Total Unrealized Losses	31	17
Less than 12 months Fair Value	1,144	736
Less than 12 months Unrealized Losses	31	17
12 months or longer Fair Value	10	0
12 months or longer Unrealized Losses	0	0
Fixed Maturities | Public Utilities | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	3,052	3,920
Total Unrealized Losses	275	178
Less than 12 months Fair Value	1,779	1,339
Less than 12 months Unrealized Losses	120	31
12 months or longer Fair Value	1,273	2,581
12 months or longer Unrealized Losses	155	147
Fixed Maturities | Sovereign and Supranational | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	33	31
Total Unrealized Losses	2	2
Less than 12 months Fair Value	0	0
Less than 12 months Unrealized Losses	0	0
12 months or longer Fair Value	33	31
12 months or longer Unrealized Losses	2	2
Fixed Maturities | Sovereign and Supranational | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	903	1,244
Total Unrealized Losses	107	84
Less than 12 months Fair Value	515	507
Less than 12 months Unrealized Losses	17	13
12 months or longer Fair Value	388	737
12 months or longer Unrealized Losses	90	71
Fixed Maturities | Banks/financial Institutions | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	347	276
Total Unrealized Losses	8	6
Less than 12 months Fair Value	318	180
Less than 12 months Unrealized Losses	7	3
12 months or longer Fair Value	29	96
12 months or longer Unrealized Losses	1	3
Fixed Maturities | Banks/financial Institutions | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	6,537	6,918
Total Unrealized Losses	926	611
Less than 12 months Fair Value	3,178	1,935
Less than 12 months Unrealized Losses	171	28
12 months or longer Fair Value	3,359	4,983
12 months or longer Unrealized Losses	755	583
Fixed Maturities | Other Corporate | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	7,478	4,534
Total Unrealized Losses	271	95
Less than 12 months Fair Value	7,350	4,404
Less than 12 months Unrealized Losses	263	86
12 months or longer Fair Value	128	130
12 months or longer Unrealized Losses	8	9
Fixed Maturities | Other Corporate | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	4,847	4,013
Total Unrealized Losses	458	261
Less than 12 months Fair Value	3,509	1,635
Less than 12 months Unrealized Losses	265	40
12 months or longer Fair Value	1,338	2,378
12 months or longer Unrealized Losses	193	221
Perpetual Securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	2,063	1,451
Total Unrealized Losses	598	170
Less than 12 months Fair Value	1,349	120
Less than 12 months Unrealized Losses	325	0
12 months or longer Fair Value	714	1,331
12 months or longer Unrealized Losses	273	170
Perpetual Securities | Dollar Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	18	136
Total Unrealized Losses	6	9
Less than 12 months Fair Value	0	120
Less than 12 months Unrealized Losses	0	0
12 months or longer Fair Value	18	16
12 months or longer Unrealized Losses	6	9
Perpetual Securities | Yen Denominated
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	2,045	1,315
Total Unrealized Losses	592	161
Less than 12 months Fair Value	1,349	0
Less than 12 months Unrealized Losses	325	0
12 months or longer Fair Value	696	1,315
12 months or longer Unrealized Losses	267	161
Equity Securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value	1	6
Total Unrealized Losses	0	1
Less than 12 months Fair Value	0	3
Less than 12 months Unrealized Losses	0	0
12 months or longer Fair Value	1	3
12 months or longer Unrealized Losses	$ 0	$ 1