INVESTMENTS - Carrying Value and Fair Value of HTM Debt Securities by Contractual Maturity Dates (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Amortized cost, net	$ 259,456	$ 268,863
Held-to-maturity Securities, Debt Maturities, Fair Value;
Fair value	231,002	243,648
Allowance for credit losses on HTM debt securities	95	120	$ 115
Mortgage-backed securities
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	20	27
After 1 but within 5 years, amortized cost	660	520
After 5 but within 10 years, amortized cost	1,229	1,496
After 10 years, amortized cost	80,996	89,579
Amortized cost, net	82,905	91,622
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	20	27
After 1 but within 5 years, fair value	622	505
After 5 but within 10 years, fair value	1,094	1,374
After 10 years, fair value	67,646	79,745
Fair value	69,382	81,651
U.S. treasury securities
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	3,403	3,148
After 1 but within 5 years, amortized cost	130,534	86,617
After 5 but within 10 years, amortized cost	997	45,196
After 10 years, amortized cost	0	0
Amortized cost, net	134,934	134,961
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	3,360	3,017
After 1 but within 5 years, fair value	117,304	79,104
After 5 but within 10 years, fair value	857	39,118
After 10 years, fair value	0	0
Fair value	121,521	121,239
State and municipal
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	30	22
After 1 but within 5 years, amortized cost	116	102
After 5 but within 10 years, amortized cost	1,289	1,002
After 10 years, amortized cost	7,668	8,111
Amortized cost, net	9,103	9,237
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	30	21
After 1 but within 5 years, fair value	113	100
After 5 but within 10 years, fair value	1,187	967
After 10 years, fair value	6,594	7,419
Fair value	7,924	8,507
Foreign government
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	1,131	143
After 1 but within 5 years, amortized cost	1,183	1,932
After 5 but within 10 years, amortized cost	0	0
After 10 years, amortized cost	0	0
Amortized cost, net	2,314	2,075
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	1,090	139
After 1 but within 5 years, fair value	1,135	1,843
After 5 but within 10 years, fair value	0	0
After 10 years, fair value	0	0
Fair value	2,225	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	1	0
After 5 but within 10 years, amortized cost	12,016	11,751
After 10 years, amortized cost	18,183	19,217
Amortized cost, net	30,200	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	1	0
After 5 but within 10 years, fair value	11,970	11,583
After 10 years, fair value	17,979	18,686
Fair value	$ 29,950	$ 30,269