INVESTMENTS - Carrying Value and Fair Value of HTM Debt Securities by Contractual Maturity Dates (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Carrying value	$ 53,320	$ 45,667
Held-to-maturity Securities, Debt Maturities, Fair Value;
Fair value	53,752	45,555
Mortgage-backed securities
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, carrying value	0	0
After 1 but within 5 years, carrying value	720	760
After 5 but within 10 years, carrying value	148	54
After 10 years, carrying value	25,231	23,830
Carrying value	26,099	24,644
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	0	0
After 1 but within 5 years, fair value	720	766
After 5 but within 10 years, fair value	149	55
After 10 years, fair value	25,235	23,810
Fair value	26,104	24,631
State and municipal securities
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, carrying value	407	406
After 1 but within 5 years, carrying value	259	112
After 5 but within 10 years, carrying value	512	363
After 10 years, carrying value	7,719	7,702
Carrying value	8,897	8,583
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	425	406
After 1 but within 5 years, fair value	270	110
After 5 but within 10 years, fair value	524	367
After 10 years, fair value	7,983	7,591
Fair value	9,202	8,474
Foreign government
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, carrying value	381	824
After 1 but within 5 years, carrying value	359	515
After 5 but within 10 years, carrying value	0	0
After 10 years, carrying value	0	0
Carrying value	740	1,339
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	381	818
After 1 but within 5 years, fair value	341	495
After 5 but within 10 years, fair value	0	0
After 10 years, fair value	0	0
Fair value	722	1,313
All other
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, carrying value	0	0
After 1 but within 5 years, carrying value	0	0
After 5 but within 10 years, carrying value	1,669	513
After 10 years, carrying value	15,915	10,588
Carrying value	17,584	11,101
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	0	0
After 1 but within 5 years, fair value	0	0
After 5 but within 10 years, fair value	1,680	514
After 10 years, fair value	16,044	10,623
Fair value	$ 17,724	$ 11,137

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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Fair value of held-to-maturity debt securities maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Carrying amount of debt securities accounted for as held-to-maturity, net of adjustments including, but not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized, and fair value hedge accounting adjustments, maturing in the fifth through tenth fiscal year following the latest fiscal year.

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Fair value of held-to-maturity debt securities maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of held-to-maturity debt securities maturing after the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Carrying amount of debt securities accounted for as held-to-maturity, net of adjustments including, but not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized, and fair value hedge accounting adjustments, maturing after the tenth fiscal year following the latest fiscal year.

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Fair value of held-to-maturity debt securities maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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