INVESTMENTS - Carrying Value and Fair Value of HTM Debt Securities by Contractual Maturity Dates (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Amortized cost	$ 242,547	$ 216,963
Held-to-maturity Securities, Debt Maturities, Fair Value;
Fair value	230,654	216,038
Allowance for credit losses on HTM debt securities	85	87	$ 78	$ 86
Mortgage-backed securities
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	79	152
After 1 but within 5 years, amortized cost	660	684
After 5 but within 10 years, amortized cost	1,641	1,655
After 10 years, amortized cost	68,360	63,200
Amortized cost	70,740	65,691
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	79	151
After 1 but within 5 years, fair value	672	725
After 5 but within 10 years, fair value	1,625	1,739
After 10 years, fair value	64,467	63,232
Fair value	66,843	65,847
U.S. treasury securities
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	79,392	65,498
After 5 but within 10 years, amortized cost	50,612	46,321
After 10 years, amortized cost	0	0
Amortized cost	130,004	111,819
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	0	0
After 1 but within 5 years, fair value	75,035	64,516
After 5 but within 10 years, fair value	47,331	45,701
After 10 years, fair value	0	0
Fair value	122,366	110,217
State and municipal
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	46	51
After 1 but within 5 years, amortized cost	174	166
After 5 but within 10 years, amortized cost	937	908
After 10 years, amortized cost	7,878	7,798
Amortized cost	9,035	8,923
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	46	50
After 1 but within 5 years, fair value	174	170
After 5 but within 10 years, fair value	942	951
After 10 years, fair value	7,822	8,329
Fair value	8,984	9,500
Foreign government
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	302	292
After 1 but within 5 years, amortized cost	1,397	1,359
After 5 but within 10 years, amortized cost	0	0
After 10 years, amortized cost	0	0
Amortized cost	1,699	1,651
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	301	291
After 1 but within 5 years, fair value	1,335	1,328
After 5 but within 10 years, fair value	0	0
After 10 years, fair value	0	0
Fair value	1,636	1,619
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	11,791	11,520
After 10 years, amortized cost	19,278	17,359
Amortized cost	31,069	28,879
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	11,729	11,515
After 10 years, fair value	19,096	17,340
Fair value	$ 30,825	$ 28,855

Amount of allowance for credit loss for debt security measured at amortized cost (held-to-maturity).

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