INVESTMENTS - Carrying Value and Fair Value of HTM Debt Securities by Contractual Maturity Dates (Details) - USD ($) $ in Millions	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Amortized cost	$ 267,592		$ 216,963
Held-to-maturity Securities, Debt Maturities, Fair Value;
Fair value	249,804		216,038
Allowance for credit losses on HTM debt securities	105	$ 85	87	$ 83	$ 78	$ 86
Mortgage-backed securities
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	15		152
After 1 but within 5 years, amortized cost	722		684
After 5 but within 10 years, amortized cost	1,563		1,655
After 10 years, amortized cost	88,142		63,200
Amortized cost	90,442		65,691
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	15		151
After 1 but within 5 years, fair value	722		725
After 5 but within 10 years, fair value	1,504		1,739
After 10 years, fair value	82,040		63,232
Fair value	84,281		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	89,460		65,498
After 5 but within 10 years, amortized cost	45,518		46,321
After 10 years, amortized cost	0		0
Amortized cost	134,978		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	83,848		64,516
After 5 but within 10 years, fair value	40,978		45,701
After 10 years, fair value	0		0
Fair value	124,826		110,217
State and municipal
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	54		51
After 1 but within 5 years, amortized cost	159		166
After 5 but within 10 years, amortized cost	919		908
After 10 years, amortized cost	7,944		7,798
Amortized cost	9,076		8,923
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	54		50
After 1 but within 5 years, fair value	160		170
After 5 but within 10 years, fair value	902		951
After 10 years, fair value	7,426		8,329
Fair value	8,542		9,500
Foreign government
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	0		292
After 1 but within 5 years, amortized cost	2,016		1,359
After 5 but within 10 years, amortized cost	0		0
After 10 years, amortized cost	0		0
Amortized cost	2,016		1,651
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	0		291
After 1 but within 5 years, fair value	1,926		1,328
After 5 but within 10 years, fair value	0		0
After 10 years, fair value	0		0
Fair value	1,926		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	11,926		11,520
After 10 years, amortized cost	19,154		17,359
Amortized cost	31,080		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	11,720		11,515
After 10 years, fair value	18,509		17,340
Fair value	$ 30,229		$ 28,855