INVESTMENTS - Carrying Value and Fair Value of HTM Debt Securities by Contractual Maturity Dates (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Carrying value	$ 66,842	$ 63,357
Held-to-maturity Securities, Debt Maturities, Fair Value;
Fair value	67,074	62,890
Mortgage-backed securities
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, carrying value	3	3
After 1 but within 5 years, carrying value	544	539
After 5 but within 10 years, carrying value	1,822	997
After 10 years, carrying value	37,654	34,407
Carrying value	40,023	35,946
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	3	3
After 1 but within 5 years, fair value	547	540
After 5 but within 10 years, fair value	1,845	1,011
After 10 years, fair value	37,736	34,024
Fair value	40,131	35,578
State and municipal securities
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, carrying value	37	37
After 1 but within 5 years, carrying value	221	168
After 5 but within 10 years, carrying value	487	540
After 10 years, carrying value	6,903	6,883
Carrying value	7,648	7,628
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	37	37
After 1 but within 5 years, fair value	228	174
After 5 but within 10 years, fair value	500	544
After 10 years, fair value	7,098	6,902
Fair value	7,863	7,657
Foreign government
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, carrying value	20	60
After 1 but within 5 years, carrying value	980	967
After 5 but within 10 years, carrying value	0	0
After 10 years, carrying value	0	0
Carrying value	1,000	1,027
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	20	36
After 1 but within 5 years, fair value	969	967
After 5 but within 10 years, fair value	0	0
After 10 years, fair value	0	0
Fair value	989	1,003
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	3,039	2,535
After 10 years, carrying value	15,132	16,221
Carrying value	18,171	18,756
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	3,041	2,539
After 10 years, fair value	15,050	16,113
Fair value	$ 18,091	$ 18,652

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

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