INVESTMENTS - Available-For-Sale Investments in Debt Securities, Perpetual Securities and Equity Securities (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	$ 69,072	$ 62,963
Gross Unrealized Gains	8,722	6,627
Gross Unrealized Losses	1,092	1,796
Fair Value	76,702	67,794
Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	66,363	60,642
Gross Unrealized Gains	8,432	6,405
Gross Unrealized Losses	1,035	1,698
Fair Value	73,760	65,349
Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,506	1,841
Gross Unrealized Gains	176	200
Gross Unrealized Losses	49	94
Fair Value	1,633	1,947
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,203	480
Gross Unrealized Gains	114	22
Gross Unrealized Losses	8	4
Fair Value	1,309	498
Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	32,459	25,592
Gross Unrealized Gains	4,951	3,067
Gross Unrealized Losses	261	148
Fair Value	37,149	28,511
Yen-denominated | Equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	624	472
Gross Unrealized Gains	83	19
Gross Unrealized Losses	2	4
Fair Value	705	487
Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	33,904	35,050
Gross Unrealized Gains	3,481	3,338
Gross Unrealized Losses	774	1,550
Fair Value	36,611	36,838
Dollar-denominated | Equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	579	8
Gross Unrealized Gains	31	3
Gross Unrealized Losses	6	0
Fair Value	604	11
Japan government and agencies | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	22,857	17,293
Gross Unrealized Gains	3,359	1,862
Gross Unrealized Losses	160	0
Fair Value	26,056	19,155
Municipalities | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,295	1,208
Municipalities | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	246	128
Gross Unrealized Gains	29	9
Gross Unrealized Losses	8	0
Fair Value	267	137
Municipalities | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	894	926
Gross Unrealized Gains	142	151
Gross Unrealized Losses	8	6
Fair Value	1,028	1,071
Mortgage- and asset-backed securities | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,337	582
Mortgage- and asset-backed securities | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,096	322
Gross Unrealized Gains	33	33
Gross Unrealized Losses	8	0
Fair Value	1,121	355
Mortgage- and asset-backed securities | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	196	200
Gross Unrealized Gains	20	27
Gross Unrealized Losses	0	0
Fair Value	216	227
Public utilities | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	7,683	7,479
Public utilities | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,533	1,400
Gross Unrealized Gains	318	210
Gross Unrealized Losses	3	10
Fair Value	1,848	1,600
Public utilities | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	5,205	5,464
Gross Unrealized Gains	690	636
Gross Unrealized Losses	60	221
Fair Value	5,835	5,879
Sovereign and supranational | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,469	1,407
Sovereign and supranational | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	862	791
Gross Unrealized Gains	186	180
Gross Unrealized Losses	5	0
Fair Value	1,043	971
Sovereign and supranational | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	335	331
Gross Unrealized Gains	91	105
Gross Unrealized Losses	0	0
Fair Value	426	436
Banks/financial institutions | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	6,063	6,019
Banks/financial institutions | Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,420	1,742
Banks/financial institutions | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	2,673	2,321
Gross Unrealized Gains	403	325
Gross Unrealized Losses	74	105
Fair Value	3,002	2,541
Banks/financial institutions | Yen-denominated | Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,266	1,581
Gross Unrealized Gains	128	143
Gross Unrealized Losses	49	93
Fair Value	1,345	1,631
Banks/financial institutions | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	2,570	2,865
Gross Unrealized Gains	507	634
Gross Unrealized Losses	16	21
Fair Value	3,061	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	24	35
Gross Unrealized Losses	0	1
Fair Value	75	111
Other corporate | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	29,699	29,378
Other corporate | Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	213	205
Other corporate | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	3,192	3,337
Gross Unrealized Gains	623	448
Gross Unrealized Losses	3	33
Fair Value	3,812	3,752
Other corporate | Yen-denominated | Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	189	183
Gross Unrealized Gains	24	22
Gross Unrealized Losses	0	0
Fair Value	213	205
Other corporate | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	24,556	25,154
Gross Unrealized Gains	2,021	1,774
Gross Unrealized Losses	690	1,302
Fair Value	25,887	25,626
U.S. Government and Agencies | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	148	110
Gross Unrealized Gains	10	11
Gross Unrealized Losses	0	0
Fair Value	$ 158	$ 121