INVESTMENTS - Carrying Value and Fair Value of HTM Debt Securities by Contractual Maturity Dates (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Amortized cost	$ 82,391	$ 80,775
Held-to-maturity Securities, Debt Maturities, Fair Value;
Fair value	83,582	82,223
Mortgage-backed securities
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	14	17
After 1 but within 5 years, amortized cost	474	458
After 5 but within 10 years, amortized cost	1,604	1,662
After 10 years, amortized cost	47,944	46,121
Amortized cost	50,036	48,258
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	14	17
After 1 but within 5 years, fair value	486	463
After 5 but within 10 years, fair value	1,757	1,729
After 10 years, fair value	49,762	47,081
Fair value	52,019	49,290
State and municipal securities
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	52	2
After 1 but within 5 years, amortized cost	89	123
After 5 but within 10 years, amortized cost	577	597
After 10 years, amortized cost	8,551	8,382
Amortized cost	9,269	9,104
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	50	26
After 1 but within 5 years, fair value	90	160
After 5 but within 10 years, fair value	604	590
After 10 years, fair value	9,016	8,755
Fair value	9,760	9,531
Foreign government
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	521	650
After 1 but within 5 years, amortized cost	1,032	1,284
After 5 but within 10 years, amortized cost	0	0
After 10 years, amortized cost	0	0
Amortized cost	1,553	1,934
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	522	652
After 1 but within 5 years, fair value	1,071	1,318
After 5 but within 10 years, fair value	0	0
After 10 years, fair value	0	0
Fair value	1,593	1,970
All other
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	0	0
After 1 but within 5 years, amortized cost	0	0
After 5 but within 10 years, amortized cost	7,092	8,545
After 10 years, amortized cost	14,441	12,934
Amortized cost	21,533	21,479
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	6,753	8,543
After 10 years, fair value	13,457	12,889
Fair value	$ 20,210	$ 21,432

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

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