INVESTMENTS - Available-For-Sale Investments in Debt Securities, Perpetual Securities and Equity Securities (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	$ 67,462	$ 62,963
Gross Unrealized Gains	9,001	6,627
Gross Unrealized Losses	1,557	1,796
Fair Value	74,906	67,794
Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	64,648	60,642
Gross Unrealized Gains	8,817	6,405
Gross Unrealized Losses	1,337	1,698
Fair Value	72,128	65,349
Perpetual securities:
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,939	1,841
Gross Unrealized Gains	142	200
Gross Unrealized Losses	172	94
Fair Value	1,909	1,947
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	875	480
Gross Unrealized Gains	42	22
Gross Unrealized Losses	48	4
Fair Value	869	498
Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	28,642	25,592
Gross Unrealized Gains	5,249	3,067
Gross Unrealized Losses	246	148
Fair Value	33,645	28,511
Yen-denominated | Equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	602	472
Gross Unrealized Gains	26	19
Gross Unrealized Losses	48	4
Fair Value	580	487
Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	36,006	35,050
Gross Unrealized Gains	3,568	3,338
Gross Unrealized Losses	1,091	1,550
Fair Value	38,483	36,838
Dollar-denominated | Equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	273	8
Gross Unrealized Gains	16	3
Gross Unrealized Losses	0	0
Fair Value	289	11
Japan government and agencies | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	19,715	17,293
Gross Unrealized Gains	3,950	1,862
Gross Unrealized Losses	0	0
Fair Value	23,665	19,155
Municipalities | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,270	1,208
Municipalities | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	142	128
Gross Unrealized Gains	36	9
Gross Unrealized Losses	0	0
Fair Value	178	137
Municipalities | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	940	926
Gross Unrealized Gains	161	151
Gross Unrealized Losses	9	6
Fair Value	1,092	1,071
Mortgage- and asset-backed securities | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	605	582
Mortgage- and asset-backed securities | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	336	322
Gross Unrealized Gains	40	33
Gross Unrealized Losses	0	0
Fair Value	376	355
Mortgage- and asset-backed securities | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	207	200
Gross Unrealized Gains	22	27
Gross Unrealized Losses	0	0
Fair Value	229	227
Public utilities | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	7,819	7,479
Public utilities | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,497	1,400
Gross Unrealized Gains	221	210
Gross Unrealized Losses	18	10
Fair Value	1,700	1,600
Public utilities | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	5,584	5,464
Gross Unrealized Gains	667	636
Gross Unrealized Losses	132	221
Fair Value	6,119	5,879
Sovereign and supranational | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,451	1,407
Sovereign and supranational | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	847	791
Gross Unrealized Gains	160	180
Gross Unrealized Losses	0	0
Fair Value	1,007	971
Sovereign and supranational | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	340	331
Gross Unrealized Gains	104	105
Gross Unrealized Losses	0	0
Fair Value	444	436
Banks/financial institutions | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	5,856	6,019
Banks/financial institutions | Perpetual securities:
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,692	1,742
Banks/financial institutions | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	2,514	2,321
Gross Unrealized Gains	326	325
Gross Unrealized Losses	156	105
Fair Value	2,684	2,541
Banks/financial institutions | Yen-denominated | Perpetual securities:
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,692	1,581
Gross Unrealized Gains	100	143
Gross Unrealized Losses	172	93
Fair Value	1,620	1,631
Banks/financial institutions | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	2,654	2,865
Gross Unrealized Gains	533	634
Gross Unrealized Losses	15	21
Fair Value	3,172	3,478
Banks/financial institutions | Dollar-denominated | Perpetual securities:
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	51	77
Gross Unrealized Gains	21	35
Gross Unrealized Losses	0	1
Fair Value	72	111
Other corporate | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	31,346	29,378
Other corporate | Perpetual securities:
Schedule of Available-for-sale Securities [Line Items]
Fair Value	217	205
Other corporate | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	3,591	3,337
Gross Unrealized Gains	516	448
Gross Unrealized Losses	72	33
Fair Value	4,035	3,752
Other corporate | Yen-denominated | Perpetual securities:
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	196	183
Gross Unrealized Gains	21	22
Gross Unrealized Losses	0	0
Fair Value	217	205
Other corporate | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	26,177	25,154
Gross Unrealized Gains	2,069	1,774
Gross Unrealized Losses	935	1,302
Fair Value	27,311	25,626
U.S. government and agencies | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	104	110
Gross Unrealized Gains	12	11
Gross Unrealized Losses	0	0
Fair Value	$ 116	$ 121