INVESTMENTS - Held-to-Maturity Investments in Debt Securities (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	$ 38,346	$ 33,459
Gross Unrealized Gains	10,507	4,278
Gross Unrealized Losses	57	217
Fair Value	48,796	37,520
Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Fair Value	48,796	37,520
Yen-denominated | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	38,346	33,459
Gross Unrealized Gains	10,507	4,278
Gross Unrealized Losses	57	217
Fair Value	48,796	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	23,440	20,004
Gross Unrealized Gains	8,636	3,387
Gross Unrealized Losses	0	0
Fair Value	32,076	23,391
Municipalities | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	398	341
Fair Value	565	415
Municipalities | Yen-denominated | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	398	341
Gross Unrealized Gains	167	74
Gross Unrealized Losses	0	0
Fair Value	565	415
Mortgage- and asset-backed securities | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	39	36
Fair Value	41	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	39	36
Gross Unrealized Gains	2	2
Gross Unrealized Losses	0	0
Fair Value	41	38
Public utilities | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	3,623	3,092
Fair Value	4,028	3,203
Public utilities | Yen-denominated | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	3,623	3,092
Gross Unrealized Gains	415	205
Gross Unrealized Losses	10	94
Fair Value	4,028	3,203
Sovereign and supranational | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	2,994	2,555
Fair Value	3,391	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	2,994	2,555
Gross Unrealized Gains	404	182
Gross Unrealized Losses	7	26
Fair Value	3,391	2,711
Banks/financial institutions | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	4,659	4,431
Fair Value	4,920	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	4,659	4,431
Gross Unrealized Gains	293	168
Gross Unrealized Losses	32	53
Fair Value	4,920	4,546
Other corporate | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	3,193	3,000
Fair Value	3,775	3,216
Other corporate | Yen-denominated | Fixed maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	3,193	3,000
Gross Unrealized Gains	590	260
Gross Unrealized Losses	8	44
Fair Value	$ 3,775	$ 3,216