INVESTMENTS - Carrying Value and Fair Value of HTM Debt Securities by Contractual Maturity Dates (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Carrying value	$ 51,527	$ 45,667
Held-to-maturity Securities, Debt Maturities, Fair Value;
Fair value	52,030	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	737	760
After 5 but within 10 years, carrying value	123	54
After 10 years, carrying value	25,209	23,830
Carrying value	26,069	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	743	766
After 5 but within 10 years, fair value	124	55
After 10 years, fair value	25,387	23,810
Fair value	26,254	24,631
State and municipal securities
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, carrying value	227	406
After 1 but within 5 years, carrying value	166	112
After 5 but within 10 years, carrying value	458	363
After 10 years, carrying value	7,707	7,702
Carrying value	8,558	8,583
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	228	406
After 1 but within 5 years, fair value	176	110
After 5 but within 10 years, fair value	474	367
After 10 years, fair value	7,928	7,591
Fair value	8,806	8,474
Foreign government
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, carrying value	413	824
After 1 but within 5 years, carrying value	171	515
After 5 but within 10 years, carrying value	0	0
After 10 years, carrying value	0	0
Carrying value	584	1,339
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	413	818
After 1 but within 5 years, fair value	157	495
After 5 but within 10 years, fair value	0	0
After 10 years, fair value	0	0
Fair value	570	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	35	0
After 5 but within 10 years, carrying value	1,146	513
After 10 years, carrying value	15,135	10,588
Carrying value	16,316	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	35	0
After 5 but within 10 years, fair value	1,148	514
After 10 years, fair value	15,217	10,623
Fair value	$ 16,400	$ 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
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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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