INVESTMENTS - Carrying Value and Fair Value of HTM Debt Securities by Contractual Maturity Dates (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Carrying value	$ 63,357	$ 53,320
Held-to-maturity Securities, Debt Maturities, Fair Value;
Fair value	62,890	53,752
Mortgage-backed securities
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, carrying value	3	0
After 1 but within 5 years, carrying value	539	720
After 5 but within 10 years, carrying value	997	148
After 10 years, carrying value	34,407	25,231
Carrying value	35,946	26,099
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	3	0
After 1 but within 5 years, fair value	540	720
After 5 but within 10 years, fair value	1,011	149
After 10 years, fair value	34,024	25,235
Fair value	35,578	26,104
State and municipal securities
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, carrying value	37	407
After 1 but within 5 years, carrying value	168	259
After 5 but within 10 years, carrying value	540	512
After 10 years, carrying value	6,883	7,719
Carrying value	7,628	8,897
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	37	425
After 1 but within 5 years, fair value	174	270
After 5 but within 10 years, fair value	544	524
After 10 years, fair value	6,902	7,983
Fair value	7,657	9,202
Foreign government
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, carrying value	60	381
After 1 but within 5 years, carrying value	967	359
After 5 but within 10 years, carrying value	0	0
After 10 years, carrying value	0	0
Carrying value	1,027	740
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	36	381
After 1 but within 5 years, fair value	967	341
After 5 but within 10 years, fair value	0	0
After 10 years, fair value	0	0
Fair value	1,003	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	2,535	1,669
After 10 years, carrying value	16,221	15,915
Carrying value	18,756	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	2,539	1,680
After 10 years, fair value	16,113	16,044
Fair value	$ 18,652	$ 17,724

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

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