INVESTMENTS - Held-to-Maturity Investments in Debt Securities (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	$ 34,262us-gaap_HeldToMaturitySecurities	$ 34,242us-gaap_HeldToMaturitySecurities
Gross Unrealized Gains	3,978	4,379
Gross Unrealized Losses	138	124
Fair Value	38,102	38,497
Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	34,262	34,242
Fair Value	38,102	38,497
Yen-denominated \| Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	34,262	34,242
Gross Unrealized Gains	3,978	4,379
Gross Unrealized Losses	138	124
Fair Value	38,102	38,497
Japan government and agencies \| Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	20,084	20,023
Fair Value	22,975	23,218
Japan government and agencies \| Yen-denominated \| Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	20,084	20,023
Gross Unrealized Gains	2,891	3,195
Gross Unrealized Losses	0	0
Fair Value	22,975	23,218
Municipalities \| Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	346	346
Fair Value	412	417
Municipalities \| Yen-denominated \| Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	346	346
Gross Unrealized Gains	66	71
Gross Unrealized Losses	0	0
Fair Value	412	417
Mortgage- and asset-backed securities \| Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	42	43
Fair Value	44	46
Mortgage- and asset-backed securities \| Yen-denominated \| Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	42	43
Gross Unrealized Gains	2	3
Gross Unrealized Losses	0	0
Fair Value	44	46
Public Utilities \| Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	3,269	3,342
Fair Value	3,503	3,603
Public Utilities \| Yen-denominated \| Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	3,269	3,342
Gross Unrealized Gains	263	281
Gross Unrealized Losses	29	20
Fair Value	3,503	3,603
Sovereign and supranational \| Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	2,564	2,556
Fair Value	2,791	2,814
Sovereign and supranational \| Yen-denominated \| Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	2,564	2,556
Gross Unrealized Gains	235	272
Gross Unrealized Losses	8	14
Fair Value	2,791	2,814
Banks/financial Institutions \| Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	4,947	4,932
Fair Value	5,054	5,085
Banks/financial Institutions \| Yen-denominated \| Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	4,947	4,932
Gross Unrealized Gains	193	231
Gross Unrealized Losses	86	78
Fair Value	5,054	5,085
Other corporate \| Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	3,010	3,000
Fair Value	3,323	3,314
Other corporate \| Yen-denominated \| Fixed Maturities
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, fixed maturities, amortized cost	3,010	3,000
Gross Unrealized Gains	328	326
Gross Unrealized Losses	15	12
Fair Value	$ 3,323	$ 3,314

Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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-Section 25

-Paragraph 1

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-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-Section 50

-Paragraph 5

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 210

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-Subparagraph (SX 210.7-03.1)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.6)

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