INVESTMENTS - Debt Securities Held-to-Maturity (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Debt Securities Held-to-maturity
Carrying value	$ 53,249	$ 53,320
Gross unrealized gains	173	702
Gross unrealized losses	1,079	270
Fair value	52,343	53,752
Mortgage-backed securities - U.S. agency-sponsored
Debt Securities Held-to-maturity
Carrying value	25,058	23,880
Gross unrealized gains	3	40
Gross unrealized losses	869	157
Fair value	24,192	23,763
Mortgage-backed securities - Alt-A
Debt Securities Held-to-maturity
Carrying value	0	141
Gross unrealized gains	0	57
Gross unrealized losses	0	0
Fair value	0	198
Mortgage-backed securities - Non-U.S. residential
Debt Securities Held-to-maturity
Carrying value	1,288	1,841
Gross unrealized gains	19	65
Gross unrealized losses	0	0
Fair value	1,307	1,906
Mortgage-backed securities - Commercial
Debt Securities Held-to-maturity
Carrying value	260	237
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair value	260	237
Mortgage-backed securities
Debt Securities Held-to-maturity
Carrying value	26,606	26,099
Gross unrealized gains	22	162
Gross unrealized losses	869	157
Fair value	25,759	26,104
State and municipal securities
Debt Securities Held-to-maturity
Carrying value	7,399	8,897
Gross unrealized gains	124	378
Gross unrealized losses	185	73
Fair value	7,338	9,202
Foreign government
Debt Securities Held-to-maturity
Carrying value	1,151	740
Gross unrealized gains	0	0
Gross unrealized losses	14	18
Fair value	1,137	722
Asset-backed securities
Debt Securities Held-to-maturity
Carrying value	18,093	17,584
Gross unrealized gains	27	162
Gross unrealized losses	11	22
Fair value	$ 18,109	$ 17,724

Amount of investment in debt security measured at amortized cost (held-to-maturity).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
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-Publisher FASB
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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 50
-Paragraph 5
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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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