INVESTMENTS - Available-For-Sale Investments in Debt Securities, Perpetual Securities and Equity Securities (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	$ 61,937	$ 60,844
Gross Unrealized Gains	8,551	8,136
Gross Unrealized Losses	581	710
Fair Value	69,907	68,270
Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	59,609	58,385
Gross Unrealized Gains	8,206	7,806
Gross Unrealized Losses	496	618
Fair Value	67,319	65,573
Perpetual securities:
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	2,309	2,440
Gross Unrealized Gains	336	321
Gross Unrealized Losses	85	92
Fair Value	2,560	2,669
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	19	19
Gross Unrealized Gains	9	9
Gross Unrealized Losses	0	0
Fair Value	28	28
Yen-denominated | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	26,371	26,501
Gross Unrealized Gains	2,938	3,029
Gross Unrealized Losses	227	242
Fair Value	29,082	29,288
Dollar-denominated | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	33,238	31,884
Gross Unrealized Gains	5,268	4,777
Gross Unrealized Losses	269	376
Fair Value	38,237	36,285
Japan government and agencies | Yen-denominated | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	17,230	17,341
Gross Unrealized Gains	1,509	1,740
Gross Unrealized Losses	0	0
Fair Value	18,739	19,081
Municipalities | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,260	1,257
Municipalities | Yen-denominated | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	88	88
Gross Unrealized Gains	7	9
Gross Unrealized Losses	0	0
Fair Value	95	97
Municipalities | Dollar-denominated | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	962	961
Gross Unrealized Gains	206	201
Gross Unrealized Losses	3	2
Fair Value	1,165	1,160
Mortgage- and asset-backed securities | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	621	602
Mortgage- and asset-backed securities | Yen-denominated | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	344	351
Gross Unrealized Gains	33	35
Gross Unrealized Losses	0	0
Fair Value	377	386
Mortgage- and asset-backed securities | Dollar-denominated | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	213	185
Gross Unrealized Gains	31	31
Gross Unrealized Losses	0	0
Fair Value	244	216
Public Utilities | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	8,218	7,897
Public Utilities | Yen-denominated | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,707	1,691
Gross Unrealized Gains	261	226
Gross Unrealized Losses	0	5
Fair Value	1,968	1,912
Public Utilities | Dollar-denominated | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	5,211	5,061
Gross Unrealized Gains	1,062	960
Gross Unrealized Losses	23	36
Fair Value	6,250	5,985
Sovereign and supranational | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,468	1,416
Sovereign and supranational | Yen-denominated | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	794	799
Gross Unrealized Gains	218	163
Gross Unrealized Losses	0	0
Fair Value	1,012	962
Sovereign and supranational | Dollar-denominated | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	340	343
Gross Unrealized Gains	116	111
Gross Unrealized Losses	0	0
Fair Value	456	454
Banks/financial Institutions | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	6,655	6,598
Banks/financial Institutions | Perpetual securities:
Schedule of Available-for-sale Securities [Line Items]
Fair Value	2,341	2,438
Banks/financial Institutions | Yen-denominated | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	2,693	2,752
Gross Unrealized Gains	321	325
Gross Unrealized Losses	190	189
Fair Value	2,824	2,888
Banks/financial Institutions | Yen-denominated | Perpetual securities:
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	2,014	2,132
Gross Unrealized Gains	249	223
Gross Unrealized Losses	84	92
Fair Value	2,179	2,263
Banks/financial Institutions | Dollar-denominated | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	3,001	2,943
Gross Unrealized Gains	835	775
Gross Unrealized Losses	5	8
Fair Value	3,831	3,710
Banks/financial Institutions | Dollar-denominated | Perpetual securities:
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	112	125
Gross Unrealized Gains	51	50
Gross Unrealized Losses	1	0
Fair Value	162	175
Other corporate | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	30,241	28,605
Other corporate | Perpetual securities:
Schedule of Available-for-sale Securities [Line Items]
Fair Value	219	231
Other corporate | Yen-denominated | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	3,515	3,479
Gross Unrealized Gains	589	531
Gross Unrealized Losses	37	48
Fair Value	4,067	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	36	48
Gross Unrealized Losses	0	0
Fair Value	219	231
Other corporate | Dollar-denominated | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	23,410	22,291
Gross Unrealized Gains	3,002	2,682
Gross Unrealized Losses	238	330
Fair Value	26,174	24,643
U.S. government and agencies | Dollar-denominated | Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	101	100
Gross Unrealized Gains	16	17
Gross Unrealized Losses	0	0
Fair Value	$ 117	$ 117