INVESTMENTS - Available-For-Sale Investments in Debt Securities, Perpetual Securities and Equity Securities (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	$ 62,963	$ 60,844
Gross Unrealized Gains	6,627	8,136
Gross Unrealized Losses	1,796	710
Fair Value	67,794	68,270
Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	60,642	58,385
Gross Unrealized Gains	6,405	7,806
Gross Unrealized Losses	1,698	618
Fair Value	65,349	65,573
Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,841	2,440
Gross Unrealized Gains	200	321
Gross Unrealized Losses	94	92
Fair Value	1,947	2,669
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	480	19
Gross Unrealized Gains	22	9
Gross Unrealized Losses	4	0
Fair Value	498	28
Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	25,592	26,501
Gross Unrealized Gains	3,067	3,029
Gross Unrealized Losses	148	242
Fair Value	28,511	29,288
Yen-denominated | Equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	472	10
Gross Unrealized Gains	19	7
Gross Unrealized Losses	4	0
Fair Value	487	17
Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	35,050	31,884
Gross Unrealized Gains	3,338	4,777
Gross Unrealized Losses	1,550	376
Fair Value	36,838	36,285
Dollar-denominated | Equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	8	9
Gross Unrealized Gains	3	2
Gross Unrealized Losses	0	0
Fair Value	11	11
Japan government and agencies | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	17,293	17,341
Gross Unrealized Gains	1,862	1,740
Gross Unrealized Losses	0	0
Fair Value	19,155	19,081
Municipalities | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,208	1,257
Municipalities | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	128	88
Gross Unrealized Gains	9	9
Gross Unrealized Losses	0	0
Fair Value	137	97
Municipalities | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	926	961
Gross Unrealized Gains	151	201
Gross Unrealized Losses	6	2
Fair Value	1,071	1,160
Mortgage- and asset-backed securities | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	582	602
Mortgage- and asset-backed securities | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	322	351
Gross Unrealized Gains	33	35
Gross Unrealized Losses	0	0
Fair Value	355	386
Mortgage- and asset-backed securities | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	200	185
Gross Unrealized Gains	27	31
Gross Unrealized Losses	0	0
Fair Value	227	216
Public utilities | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	7,479	7,897
Public utilities | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,400	1,691
Gross Unrealized Gains	210	226
Gross Unrealized Losses	10	5
Fair Value	1,600	1,912
Public utilities | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	5,464	5,061
Gross Unrealized Gains	636	960
Gross Unrealized Losses	221	36
Fair Value	5,879	5,985
Sovereign and supranational | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,407	1,416
Sovereign and supranational | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	791	799
Gross Unrealized Gains	180	163
Gross Unrealized Losses	0	0
Fair Value	971	962
Sovereign and supranational | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	331	343
Gross Unrealized Gains	105	111
Gross Unrealized Losses	0	0
Fair Value	436	454
Banks/financial institutions | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	6,019	6,598
Banks/financial institutions | Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,742	2,438
Banks/financial institutions | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	2,321	2,752
Gross Unrealized Gains	325	325
Gross Unrealized Losses	105	189
Fair Value	2,541	2,888
Banks/financial institutions | Yen-denominated | Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,581	2,132
Gross Unrealized Gains	143	223
Gross Unrealized Losses	93	92
Fair Value	1,631	2,263
Banks/financial institutions | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	2,865	2,943
Gross Unrealized Gains	634	775
Gross Unrealized Losses	21	8
Fair Value	3,478	3,710
Banks/financial institutions | Dollar-denominated | Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	77	125
Gross Unrealized Gains	35	50
Gross Unrealized Losses	1	0
Fair Value	111	175
Other corporate | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	29,378	28,605
Other corporate | Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	205	231
Other corporate | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	3,337	3,479
Gross Unrealized Gains	448	531
Gross Unrealized Losses	33	48
Fair Value	3,752	3,962
Other corporate | Yen-denominated | Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	183	183
Gross Unrealized Gains	22	48
Gross Unrealized Losses	0	0
Fair Value	205	231
Other corporate | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	25,154	22,291
Gross Unrealized Gains	1,774	2,682
Gross Unrealized Losses	1,302	330
Fair Value	25,626	24,643
U.S. Government and Agencies | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	110	100
Gross Unrealized Gains	11	17
Gross Unrealized Losses	0	0
Fair Value	$ 121	$ 117