INVESTMENTS - Available-For-Sale Investments in Debt Securities, Perpetual Securities and Equity Securities (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	$ 73,160	$ 62,963
Gross Unrealized Gains	11,518	6,627
Gross Unrealized Losses	1,363	1,796
Fair Value	83,315	67,794
Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	69,999	60,642
Gross Unrealized Gains	11,357	6,405
Gross Unrealized Losses	1,070	1,698
Fair Value	80,286	65,349
Perpetual securities:
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,916	1,841
Gross Unrealized Gains	115	200
Gross Unrealized Losses	199	94
Fair Value	1,832	1,947
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,245	480
Gross Unrealized Gains	46	22
Gross Unrealized Losses	94	4
Fair Value	1,197	498
Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	32,442	25,592
Gross Unrealized Gains	7,437	3,067
Gross Unrealized Losses	187	148
Fair Value	39,692	28,511
Yen-denominated | Equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	694	472
Gross Unrealized Gains	29	19
Gross Unrealized Losses	76	4
Fair Value	647	487
Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	37,557	35,050
Gross Unrealized Gains	3,920	3,338
Gross Unrealized Losses	883	1,550
Fair Value	40,594	36,838
Dollar-denominated | Equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	551	8
Gross Unrealized Gains	17	3
Gross Unrealized Losses	18	0
Fair Value	550	11
Japan government and agencies | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	22,176	17,293
Gross Unrealized Gains	5,828	1,862
Gross Unrealized Losses	0	0
Fair Value	28,004	19,155
Municipalities | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,360	1,208
Municipalities | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	200	128
Gross Unrealized Gains	60	9
Gross Unrealized Losses	0	0
Fair Value	260	137
Municipalities | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	943	926
Gross Unrealized Gains	164	151
Gross Unrealized Losses	7	6
Fair Value	1,100	1,071
Mortgage- and asset-backed securities | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,138	582
Mortgage- and asset-backed securities | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	870	322
Gross Unrealized Gains	51	33
Gross Unrealized Losses	0	0
Fair Value	921	355
Mortgage- and asset-backed securities | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	199	200
Gross Unrealized Gains	18	27
Gross Unrealized Losses	0	0
Fair Value	217	227
Public utilities | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	8,327	7,479
Public utilities | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,639	1,400
Gross Unrealized Gains	277	210
Gross Unrealized Losses	13	10
Fair Value	1,903	1,600
Public utilities | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	5,724	5,464
Gross Unrealized Gains	776	636
Gross Unrealized Losses	76	221
Fair Value	6,424	5,879
Sovereign and supranational | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,565	1,407
Sovereign and supranational | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	927	791
Gross Unrealized Gains	189	180
Gross Unrealized Losses	0	0
Fair Value	1,116	971
Sovereign and supranational | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	352	331
Gross Unrealized Gains	97	105
Gross Unrealized Losses	0	0
Fair Value	449	436
Banks/financial institutions | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	6,226	6,019
Banks/financial institutions | Perpetual securities:
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,598	1,742
Banks/financial institutions | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	2,704	2,321
Gross Unrealized Gains	382	325
Gross Unrealized Losses	119	105
Fair Value	2,967	2,541
Banks/financial institutions | Yen-denominated | Perpetual securities:
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,650	1,581
Gross Unrealized Gains	77	143
Gross Unrealized Losses	199	93
Fair Value	1,528	1,631
Banks/financial institutions | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	2,742	2,865
Gross Unrealized Gains	533	634
Gross Unrealized Losses	16	21
Fair Value	3,259	3,478
Banks/financial institutions | Dollar-denominated | Perpetual securities:
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	52	77
Gross Unrealized Gains	18	35
Gross Unrealized Losses	0	1
Fair Value	70	111
Other corporate | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	33,527	29,378
Other corporate | Perpetual securities:
Schedule of Available-for-sale Securities [Line Items]
Fair Value	234	205
Other corporate | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	3,926	3,337
Gross Unrealized Gains	650	448
Gross Unrealized Losses	55	33
Fair Value	4,521	3,752
Other corporate | Yen-denominated | Perpetual securities:
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	214	183
Gross Unrealized Gains	20	22
Gross Unrealized Losses	0	0
Fair Value	234	205
Other corporate | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	27,474	25,154
Gross Unrealized Gains	2,316	1,774
Gross Unrealized Losses	784	1,302
Fair Value	29,006	25,626
U.S. government and agencies | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	123	110
Gross Unrealized Gains	16	11
Gross Unrealized Losses	0	0
Fair Value	$ 139	$ 121