INVESTMENTS - Carrying Value and Fair Value of HTM Debt Securities by Contractual Maturity Dates (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Held-to-maturity Securities, Debt Maturities, Amortized Cost
Total amortized cost	$ 254,247	$ 268,863
Held-to-maturity Securities, Debt Maturities, Fair Value
Fair value	$ 235,001	243,648
Held-to-maturity Securities, Debt Maturities, Weighted Average Yield
Total	2.33%
Allowance for credit losses on HTM debt securities	$ 95	120	$ 87
Mortgage-backed securities
Held-to-maturity Securities, Debt Maturities, Amortized Cost
Due within 1 year, amortized cost	20
After 1 but within 5 years, amortized cost	1,213
After 5 but within 10 years, amortized cost	708
After 10 years, amortized cost	79,092
Total amortized cost	81,033	91,622
Held-to-maturity Securities, Debt Maturities, Fair Value
Due within 1 year, fair value	20
After 1 but within 5 years, fair value	1,156
After 5 but within 10 years, fair value	650
After 10 years, fair value	70,457
Fair value	$ 72,283	81,651
Held-to-maturity Securities, Debt Maturities, Weighted Average Yield
Due within 1 year, weighted average yield	2.14%
After 1 but within 5 years, weighted average yield	3.46%
After 5 but within 10 years, weighted average yield	2.47%
After 10 years, weighted average yield	2.88%
Total	2.89%
US Treasury securities
Held-to-maturity Securities, Debt Maturities, Amortized Cost
Due within 1 year, amortized cost	$ 5,607
After 1 but within 5 years, amortized cost	126,169
After 5 but within 10 years, amortized cost	0
After 10 years, amortized cost	0
Total amortized cost	131,776	134,961
Held-to-maturity Securities, Debt Maturities, Fair Value
Due within 1 year, fair value	5,424
After 1 but within 5 years, fair value	116,444
After 5 but within 10 years, fair value	0
After 10 years, fair value	0
Fair value	$ 121,868	121,239
Held-to-maturity Securities, Debt Maturities, Weighted Average Yield
Due within 1 year, weighted average yield	0.68%
After 1 but within 5 years, weighted average yield	1.10%
After 5 but within 10 years, weighted average yield	0.00%
After 10 years, weighted average yield	0.00%
Total	1.08%
State and municipal
Held-to-maturity Securities, Debt Maturities, Amortized Cost
Due within 1 year, amortized cost	$ 34
After 1 but within 5 years, amortized cost	117
After 5 but within 10 years, amortized cost	1,388
After 10 years, amortized cost	7,643
Total amortized cost	9,182	9,237
Held-to-maturity Securities, Debt Maturities, Fair Value
Due within 1 year, fair value	34
After 1 but within 5 years, fair value	115
After 5 but within 10 years, fair value	1,351
After 10 years, fair value	7,278
Fair value	$ 8,778	8,507
Held-to-maturity Securities, Debt Maturities, Weighted Average Yield
Due within 1 year, weighted average yield	3.13%
After 1 but within 5 years, weighted average yield	3.04%
After 5 but within 10 years, weighted average yield	3.14%
After 10 years, weighted average yield	3.34%
Total	3.31%
Foreign government
Held-to-maturity Securities, Debt Maturities, Amortized Cost
Due within 1 year, amortized cost	$ 1,553
After 1 but within 5 years, amortized cost	657
After 5 but within 10 years, amortized cost	0
After 10 years, amortized cost	0
Total amortized cost	2,210	2,075
Held-to-maturity Securities, Debt Maturities, Fair Value
Due within 1 year, fair value	1,493
After 1 but within 5 years, fair value	659
After 5 but within 10 years, fair value	0
After 10 years, fair value	0
Fair value	$ 2,152	$ 1,982
Held-to-maturity Securities, Debt Maturities, Weighted Average Yield
Due within 1 year, weighted average yield	10.77%
After 1 but within 5 years, weighted average yield	9.82%
After 5 but within 10 years, weighted average yield	0.00%
After 10 years, weighted average yield	0.00%
Total	10.49%
All other
Held-to-maturity Securities, Debt Maturities, Amortized Cost
Due within 1 year, amortized cost	$ 0
After 1 but within 5 years, amortized cost	1
After 5 but within 10 years, amortized cost	11,365
After 10 years, amortized cost	18,680
Total amortized cost	30,046
Held-to-maturity Securities, Debt Maturities, Fair Value
Due within 1 year, fair value	0
After 1 but within 5 years, fair value	1
After 5 but within 10 years, fair value	11,362
After 10 years, fair value	18,557
Fair value	$ 29,920
Held-to-maturity Securities, Debt Maturities, Weighted Average Yield
Due within 1 year, weighted average yield	0.00%
After 1 but within 5 years, weighted average yield	1.22%
After 5 but within 10 years, weighted average yield	4.97%
After 10 years, weighted average yield	5.70%
Total	5.42%