FAIR VALUE MEASUREMENTS - Fair Value Hierarchy Levels of Assets and Liabilities Carried at Cost or Amortized Cost (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Assets:
Cost or Amortized Cost	$ 45,204	$ 54,426
Liabilities:
Notes Payable	4,276	4,343
Notes payable (excluding capital leases), fair value	4,924	4,992
Obligation To Japanese Policyholder Protection Corporation Carrying Value	2	23
Obligation to Japanese Policyholder Protection Corporation Fair Value Disclosure	2	23
Total Financial Instrument Liabilities Not Carried At Fair Value	4,278	4,366
Liabilities Fair Value Disclosure Financial Instruments Carried At Cost	4,926	5,015
Fixed Maturities
Assets:
Cost or Amortized Cost	45,204	54,426
Held-to-maturity securities, fair value	47,047	54,841
Japan government and agencies | Fixed Maturities
Assets:
Cost or Amortized Cost	24,606	32,043
Held-to-maturity securities, fair value	26,760	32,332
Municipalities | Fixed Maturities
Assets:
Cost or Amortized Cost	452	492
Held-to-maturity securities, fair value	517	520
Mortgage- and asset-backed Securities | Fixed Maturities
Assets:
Cost or Amortized Cost	77	90
Held-to-maturity securities, fair value	81	94
Public Utilities | Fixed Maturities
Assets:
Cost or Amortized Cost	4,532	4,924
Held-to-maturity securities, fair value	4,512	5,051
Sovereign and Supranational | Fixed Maturities
Assets:
Cost or Amortized Cost	2,953	3,209
Held-to-maturity securities, fair value	3,073	3,317
Banks/financial Institutions | Fixed Maturities
Assets:
Cost or Amortized Cost	8,480	9,211
Held-to-maturity securities, fair value	7,953	8,991
Other Corporate | Fixed Maturities
Assets:
Cost or Amortized Cost	4,104	4,457
Held-to-maturity securities, fair value	4,151	4,536
Level 1
Liabilities:
Notes payable (excluding capital leases), fair value	0	0
Obligation to Japanese Policyholder Protection Corporation Fair Value Disclosure	0	0
Liabilities Fair Value Disclosure Financial Instruments Carried At Cost	0	0
Level 1 | Fixed Maturities
Assets:
Held-to-maturity securities, fair value	26,760	32,332
Level 1 | Japan government and agencies | Fixed Maturities
Assets:
Held-to-maturity securities, fair value	26,760	32,332
Level 1 | Municipalities | Fixed Maturities
Assets:
Held-to-maturity securities, fair value	0	0
Level 1 | Mortgage- and asset-backed Securities | Fixed Maturities
Assets:
Held-to-maturity securities, fair value	0	0
Level 1 | Public Utilities | Fixed Maturities
Assets:
Held-to-maturity securities, fair value	0	0
Level 1 | Sovereign and Supranational | Fixed Maturities
Assets:
Held-to-maturity securities, fair value	0	0
Level 1 | Banks/financial Institutions | Fixed Maturities
Assets:
Held-to-maturity securities, fair value	0	0
Level 1 | Other Corporate | Fixed Maturities
Assets:
Held-to-maturity securities, fair value	0	0
Level 2
Liabilities:
Notes payable (excluding capital leases), fair value	0	0
Obligation to Japanese Policyholder Protection Corporation Fair Value Disclosure	0	0
Liabilities Fair Value Disclosure Financial Instruments Carried At Cost	0	0
Level 2 | Fixed Maturities
Assets:
Held-to-maturity securities, fair value	20,232	22,445
Level 2 | Japan government and agencies | Fixed Maturities
Assets:
Held-to-maturity securities, fair value	0	0
Level 2 | Municipalities | Fixed Maturities
Assets:
Held-to-maturity securities, fair value	517	520
Level 2 | Mortgage- and asset-backed Securities | Fixed Maturities
Assets:
Held-to-maturity securities, fair value	26	30
Level 2 | Public Utilities | Fixed Maturities
Assets:
Held-to-maturity securities, fair value	4,512	5,051
Level 2 | Sovereign and Supranational | Fixed Maturities
Assets:
Held-to-maturity securities, fair value	3,073	3,317
Level 2 | Banks/financial Institutions | Fixed Maturities
Assets:
Held-to-maturity securities, fair value	7,953	8,991
Level 2 | Other Corporate | Fixed Maturities
Assets:
Held-to-maturity securities, fair value	4,151	4,536
Level 3
Liabilities:
Notes payable (excluding capital leases), fair value	4,924	4,992
Obligation to Japanese Policyholder Protection Corporation Fair Value Disclosure	2	23
Liabilities Fair Value Disclosure Financial Instruments Carried At Cost	4,926	5,015
Level 3 | Fixed Maturities
Assets:
Held-to-maturity securities, fair value	55	64
Level 3 | Japan government and agencies | Fixed Maturities
Assets:
Held-to-maturity securities, fair value	0	0
Level 3 | Municipalities | Fixed Maturities
Assets:
Held-to-maturity securities, fair value	0	0
Level 3 | Mortgage- and asset-backed Securities | Fixed Maturities
Assets:
Held-to-maturity securities, fair value	55	64
Level 3 | Public Utilities | Fixed Maturities
Assets:
Held-to-maturity securities, fair value	0	0
Level 3 | Sovereign and Supranational | Fixed Maturities
Assets:
Held-to-maturity securities, fair value	0	0
Level 3 | Banks/financial Institutions | Fixed Maturities
Assets:
Held-to-maturity securities, fair value	0	0
Level 3 | Other Corporate | Fixed Maturities
Assets:
Held-to-maturity securities, fair value	$ 0	$ 0