INVESTMENTS - Available-For-Sale Investments in Debt Securities, Perpetual Securities and Equity Securities (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	$ 74,807	$ 69,072
Gross Unrealized Gains	9,355	8,722
Gross Unrealized Losses	1,159	1,092
Fair Value	83,003	76,702
Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	71,958	66,363
Gross Unrealized Gains	8,908	8,432
Gross Unrealized Losses	1,109	1,035
Fair Value	79,757	73,760
Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,560	1,506
Gross Unrealized Gains	314	176
Gross Unrealized Losses	31	49
Fair Value	1,843	1,633
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,289	1,203
Gross Unrealized Gains	133	114
Gross Unrealized Losses	19	8
Fair Value	1,403	1,309
Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	37,529	32,459
Gross Unrealized Gains	5,042	4,951
Gross Unrealized Losses	499	261
Fair Value	42,072	37,149
Yen-denominated | Equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	668	624
Gross Unrealized Gains	86	83
Gross Unrealized Losses	5	2
Fair Value	749	705
Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	34,429	33,904
Gross Unrealized Gains	3,866	3,481
Gross Unrealized Losses	610	774
Fair Value	37,685	36,611
Dollar-denominated | Equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	621	579
Gross Unrealized Gains	47	31
Gross Unrealized Losses	14	6
Fair Value	654	604
Japan government and agencies | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	27,020	22,857
Gross Unrealized Gains	3,262	3,359
Gross Unrealized Losses	396	160
Fair Value	29,886	26,056
Municipalities | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,344	1,295
Municipalities | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	305	246
Gross Unrealized Gains	26	29
Gross Unrealized Losses	14	8
Fair Value	317	267
Municipalities | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	891	894
Gross Unrealized Gains	143	142
Gross Unrealized Losses	7	8
Fair Value	1,027	1,028
Mortgage- and asset-backed securities | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	480	1,337
Mortgage- and asset-backed securities | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	261	1,096
Gross Unrealized Gains	31	33
Gross Unrealized Losses	0	8
Fair Value	292	1,121
Mortgage- and asset-backed securities | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	175	196
Gross Unrealized Gains	13	20
Gross Unrealized Losses	0	0
Fair Value	188	216
Public utilities | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	8,004	7,683
Public utilities | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,654	1,533
Gross Unrealized Gains	367	318
Gross Unrealized Losses	8	3
Fair Value	2,013	1,848
Public utilities | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	5,263	5,205
Gross Unrealized Gains	770	690
Gross Unrealized Losses	42	60
Fair Value	5,991	5,835
Sovereign and supranational | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	2,074	1,469
Sovereign and supranational | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,482	862
Gross Unrealized Gains	181	186
Gross Unrealized Losses	3	5
Fair Value	1,660	1,043
Sovereign and supranational | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	326	335
Gross Unrealized Gains	88	91
Gross Unrealized Losses	0	0
Fair Value	414	426
Banks/financial institutions | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	6,796	6,063
Banks/financial institutions | Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,615	1,420
Banks/financial institutions | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	3,150	2,673
Gross Unrealized Gains	460	403
Gross Unrealized Losses	64	74
Fair Value	3,546	3,002
Banks/financial institutions | Yen-denominated | Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,317	1,266
Gross Unrealized Gains	256	128
Gross Unrealized Losses	31	49
Fair Value	1,542	1,345
Banks/financial institutions | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	2,684	2,570
Gross Unrealized Gains	573	507
Gross Unrealized Losses	7	16
Fair Value	3,250	3,061
Banks/financial institutions | Dollar-denominated | Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	46	51
Gross Unrealized Gains	27	24
Gross Unrealized Losses	0	0
Fair Value	73	75
Other corporate | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	31,030	29,699
Other corporate | Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	228	213
Other corporate | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	3,657	3,192
Gross Unrealized Gains	715	623
Gross Unrealized Losses	14	3
Fair Value	4,358	3,812
Other corporate | Yen-denominated | Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	197	189
Gross Unrealized Gains	31	24
Gross Unrealized Losses	0	0
Fair Value	228	213
Other corporate | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	24,959	24,556
Gross Unrealized Gains	2,267	2,021
Gross Unrealized Losses	554	690
Fair Value	26,672	25,887
U.S. government and agencies | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	131	148
Gross Unrealized Gains	12	10
Gross Unrealized Losses	0	0
Fair Value	$ 143	$ 158