FAIR VALUE MEASUREMENT - Estimate Fair Value of Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Assets
Loans	$ 8,526		$ 7,594
Liabilities
Deposits(5)	1,278,137		1,308,681
Allowance for credit losses	18,216	$ 18,296	18,145	$ 17,496	$ 17,169	$ 16,974
Loans, net of unearned income	687,722		689,362
Corporate loans
Assets
Loans	8,232		7,281
Liabilities
Allowance for credit losses	2,484	$ 2,772	2,714	$ 2,630	$ 2,780	$ 2,855
Loans, net of unearned income	301,605		300,165
Carrying value
Assets
HTM debt securities, net of allowance(1)	256,500		259,700
Securities borrowed and purchased under agreements to resell	139,900		139,600
Loans	660,700		663,300
Other financial assets	342,500		347,500
Liabilities
Deposits(5)	1,274,700		1,306,200
Securities loaned and sold under agreements to repurchase	235,400		215,600
Long-term debt	170,800		170,300
Other financial liabilities	139,900		132,800
Allowance for credit losses	18,200		18,100
Estimated fair value
Assets
HTM debt securities, net of allowance(1)	235,800		240,600
Securities borrowed and purchased under agreements to resell	139,900		139,700
Loans	663,800		673,200
Other financial assets	342,500		347,500
Liabilities
Deposits(5)	1,274,600		1,305,900
Securities loaned and sold under agreements to repurchase	235,400		215,600
Long-term debt	174,000		173,400
Other financial liabilities	139,900		132,800
Estimated fair value | Corporate loans
Liabilities
Loans, net of unearned income	8,232		7,281
Estimated fair value | Level 1
Assets
HTM debt securities, net of allowance(1)	124,600		124,000
Securities borrowed and purchased under agreements to resell	0		0
Loans	0		0
Other financial assets	228,400		243,100
Liabilities
Deposits(5)	0		0
Securities loaned and sold under agreements to repurchase	0		0
Long-term debt	0		0
Other financial liabilities	0		0
Estimated fair value | Level 2
Assets
HTM debt securities, net of allowance(1)	108,700		114,100
Securities borrowed and purchased under agreements to resell	139,900		139,700
Loans	0		0
Other financial assets	17,800		17,800
Liabilities
Deposits(5)	1,274,600		1,116,500
Securities loaned and sold under agreements to repurchase	235,400		215,600
Long-term debt	169,800		168,000
Other financial liabilities	25,100		29,200
Estimated fair value | Level 3
Assets
HTM debt securities, net of allowance(1)	2,500		2,500
Securities borrowed and purchased under agreements to resell	0		0
Loans	663,800		673,200
Other financial assets	96,300		86,600
Liabilities
Deposits(5)	0		189,400
Securities loaned and sold under agreements to repurchase	0		0
Long-term debt	4,200		5,400
Other financial liabilities	114,800		103,600
Estimated fair value | Level 3 | Corporate loans
Fair value measurements additional disclosures
Unfunded lending commitments	13,000		14,200
Lease financing
Liabilities
Loans, net of unearned income	300		300
Lease financing | Corporate loans
Liabilities
Loans, net of unearned income	$ 267		$ 275