INVESTMENTS - Carrying Value and Fair Value of HTM Debt Securities by Contractual Maturity Dates (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Carrying value	$ 52,492	$ 53,320
Held-to-maturity Securities, Debt Maturities, Fair Value;
Fair value	52,100	53,752
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	131	720
After 5 but within 10 years, carrying value	166	148
After 10 years, carrying value	25,385	25,231
Carrying value	25,682	26,099
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	0	0
After 1 but within 5 years, fair value	130	720
After 5 but within 10 years, fair value	165	149
After 10 years, fair value	24,867	25,235
Fair value	25,162	26,104
State and municipal securities
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, carrying value	234	407
After 1 but within 5 years, carrying value	380	259
After 5 but within 10 years, carrying value	438	512
After 10 years, carrying value	6,601	7,719
Carrying value	7,653	8,897
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	234	425
After 1 but within 5 years, fair value	398	270
After 5 but within 10 years, fair value	442	524
After 10 years, fair value	6,632	7,983
Fair value	7,706	9,202
Foreign government
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, carrying value	486	381
After 1 but within 5 years, carrying value	868	359
After 5 but within 10 years, carrying value	0	0
After 10 years, carrying value	0	0
Carrying value	1,354	740
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	486	381
After 1 but within 5 years, fair value	859	341
After 5 but within 10 years, fair value	0	0
After 10 years, fair value	0	0
Fair value	1,345	722
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	1,989	1,669
After 10 years, carrying value	15,814	15,915
Carrying value	17,803	17,584
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	1,994	1,680
After 10 years, fair value	15,893	16,044
Fair value	$ 17,887	$ 17,724

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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-Name Accounting Standards Codification
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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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