INVESTMENTS - Held-to-Maturity Investments in Debt Securities (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule of Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	$ 45,204	$ 54,426
Gross Unrealized Gains	3,057	1,213
Gross Unrealized Losses	1,214	798
Fair Value	47,047	54,841
Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	45,204	54,426
Yen Denominated | Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	45,204	54,426
Gross Unrealized Gains	3,057	1,213
Gross Unrealized Losses	1,214	798
Fair Value	47,047	54,841
Japan government and agencies | Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	24,606	32,043
Japan government and agencies | Yen Denominated | Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	24,606	32,043
Gross Unrealized Gains	2,154	356
Gross Unrealized Losses	0	67
Fair Value	26,760	32,332
Municipalities | Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	452	492
Municipalities | Yen Denominated | Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	452	492
Gross Unrealized Gains	65	30
Gross Unrealized Losses	0	2
Fair Value	517	520
Mortgage- and asset-backed Securities | Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	77	90
Mortgage- and asset-backed Securities | Yen Denominated | Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	77	90
Gross Unrealized Gains	4	4
Gross Unrealized Losses	0	0
Fair Value	81	94
Public Utilities | Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	4,532	4,924
Public Utilities | Yen Denominated | Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	4,532	4,924
Gross Unrealized Gains	202	233
Gross Unrealized Losses	222	106
Fair Value	4,512	5,051
Sovereign and Supranational | Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	2,953	3,209
Sovereign and Supranational | Yen Denominated | Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	2,953	3,209
Gross Unrealized Gains	220	192
Gross Unrealized Losses	100	84
Fair Value	3,073	3,317
Banks/financial Institutions | Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	8,480	9,211
Banks/financial Institutions | Yen Denominated | Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	8,480	9,211
Gross Unrealized Gains	163	211
Gross Unrealized Losses	690	431
Fair Value	7,953	8,991
Other Corporate | Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	4,104	4,457
Other Corporate | Yen Denominated | Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Cost or Amortized Cost	4,104	4,457
Gross Unrealized Gains	249	187
Gross Unrealized Losses	202	108
Fair Value	$ 4,151	$ 4,536