INVESTMENTS - Held-to-Maturity Investments in Debt Securities (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	$ 35,515	$ 33,459
Gross Unrealized Gains	7,464	4,278
Gross Unrealized Losses	172	217
Fair Value	42,807	37,520
Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Fair Value	42,807	37,520
Yen-denominated | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	35,515	33,459
Gross Unrealized Gains	7,464	4,278
Gross Unrealized Losses	172	217
Fair Value	42,807	37,520
Japan government and agencies | Yen-denominated | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	21,409	20,004
Gross Unrealized Gains	6,186	3,387
Gross Unrealized Losses	0	0
Fair Value	27,595	23,391
Municipalities | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	365	341
Fair Value	487	415
Municipalities | Yen-denominated | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	365	341
Gross Unrealized Gains	122	74
Gross Unrealized Losses	0	0
Fair Value	487	415
Mortgage- and asset-backed securities | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	37	36
Fair Value	40	38
Mortgage- and asset-backed securities | Yen-denominated | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	37	36
Gross Unrealized Gains	3	2
Gross Unrealized Losses	0	0
Fair Value	40	38
Public utilities | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	3,309	3,092
Fair Value	3,520	3,203
Public utilities | Yen-denominated | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	3,309	3,092
Gross Unrealized Gains	282	205
Gross Unrealized Losses	71	94
Fair Value	3,520	3,203
Sovereign and supranational | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	2,735	2,555
Fair Value	2,987	2,711
Sovereign and supranational | Yen-denominated | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	2,735	2,555
Gross Unrealized Gains	263	182
Gross Unrealized Losses	11	26
Fair Value	2,987	2,711
Banks/financial institutions | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	4,566	4,431
Fair Value	4,731	4,546
Banks/financial institutions | Yen-denominated | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	4,566	4,431
Gross Unrealized Gains	215	168
Gross Unrealized Losses	50	53
Fair Value	4,731	4,546
Other corporate | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	3,094	3,000
Fair Value	3,447	3,216
Other corporate | Yen-denominated | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	3,094	3,000
Gross Unrealized Gains	393	260
Gross Unrealized Losses	40	44
Fair Value	$ 3,447	$ 3,216