INVESTMENTS - Carrying Value and Fair Value of HTM Debt Securities by Contractual Maturity Dates (Details) - USD ($) $ in Millions	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Amortized cost, net	$ 262,066		$ 268,863
Held-to-maturity Securities, Debt Maturities, Fair Value;
Fair value	238,021		243,648
Allowance for credit losses on HTM debt securities	99	$ 104	120	$ 105	$ 85	$ 87
Mortgage-backed securities
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	15		27
After 1 but within 5 years, amortized cost	690		520
After 5 but within 10 years, amortized cost	1,254		1,496
After 10 years, amortized cost	83,089		89,579
Amortized cost, net	85,048		91,622
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	15		27
After 1 but within 5 years, fair value	655		505
After 5 but within 10 years, fair value	1,141		1,374
After 10 years, fair value	73,386		79,745
Fair value	75,197		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	120,838		86,617
After 5 but within 10 years, amortized cost	10,957		45,196
After 10 years, amortized cost	0		0
Amortized cost, net	134,944		134,961
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	3,077		3,017
After 1 but within 5 years, fair value	109,351		79,104
After 5 but within 10 years, fair value	9,425		39,118
After 10 years, fair value	0		0
Fair value	121,853		121,239
State and municipal
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	36		22
After 1 but within 5 years, amortized cost	104		102
After 5 but within 10 years, amortized cost	1,222		1,002
After 10 years, amortized cost	7,819		8,111
Amortized cost, net	9,181		9,237
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	35		21
After 1 but within 5 years, fair value	102		100
After 5 but within 10 years, fair value	1,183		967
After 10 years, fair value	7,268		7,419
Fair value	8,588		8,507
Foreign government
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	163		143
After 1 but within 5 years, amortized cost	2,197		1,932
After 5 but within 10 years, amortized cost	0		0
After 10 years, amortized cost	0		0
Amortized cost, net	2,360		2,075
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	161		139
After 1 but within 5 years, fair value	2,106		1,843
After 5 but within 10 years, fair value	0		0
After 10 years, fair value	0		0
Fair value	2,267		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	12,232		11,751
After 10 years, amortized cost	18,301		19,217
Amortized cost, net	30,533		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	12,141		11,583
After 10 years, fair value	17,975		18,686
Fair value	$ 30,116		$ 30,269