INVESTMENTS - Carrying Value and Fair Value of HTM Debt Securities by Contractual Maturity Dates (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Amortized cost, net	$ 264,342	$ 268,863
Held-to-maturity Securities, Debt Maturities, Fair Value;
Fair value	242,851	243,648
Allowance for credit losses on HTM debt securities	104	120	$ 85	$ 87
Mortgage-backed securities
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	27	27
After 1 but within 5 years, amortized cost	634	520
After 5 but within 10 years, amortized cost	1,347	1,496
After 10 years, amortized cost	85,100	89,579
Amortized cost, net	87,108	91,622
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	27	27
After 1 but within 5 years, fair value	611	505
After 5 but within 10 years, fair value	1,246	1,374
After 10 years, fair value	76,468	79,745
Fair value	78,352	81,651
U.S. treasury securities
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	3,149	3,148
After 1 but within 5 years, amortized cost	111,568	86,617
After 5 but within 10 years, amortized cost	20,235	45,196
After 10 years, amortized cost	0	0
Amortized cost, net	134,952	134,961
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	3,051	3,017
After 1 but within 5 years, fair value	102,525	79,104
After 5 but within 10 years, fair value	17,871	39,118
After 10 years, fair value	0	0
Fair value	123,447	121,239
State and municipal
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	27	22
After 1 but within 5 years, amortized cost	112	102
After 5 but within 10 years, amortized cost	1,085	1,002
After 10 years, amortized cost	7,988	8,111
Amortized cost, net	9,212	9,237
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	27	21
After 1 but within 5 years, fair value	111	100
After 5 but within 10 years, fair value	1,063	967
After 10 years, fair value	7,518	7,419
Fair value	8,719	8,507
Foreign government
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	155	143
After 1 but within 5 years, amortized cost	2,089	1,932
After 5 but within 10 years, amortized cost	0	0
After 10 years, amortized cost	0	0
Amortized cost, net	2,244	2,075
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	151	139
After 1 but within 5 years, fair value	1,990	1,843
After 5 but within 10 years, fair value	0	0
After 10 years, fair value	0	0
Fair value	2,141	1,982
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	11,919	11,751
After 10 years, amortized cost	18,907	19,217
Amortized cost, net	30,826	30,968
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	11,783	11,583
After 10 years, fair value	18,409	18,686
Fair value	$ 30,192	$ 30,269