FAIR VALUE MEASUREMENT - Estimate Fair Value of Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2024	Jun. 30, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022
Assets
Loans	$ 8,106		$ 7,594
Liabilities
Deposits	1,309,999		1,308,681
Allowance for credit losses	18,356	$ 18,216	18,145	$ 17,629	$ 17,496	$ 16,974
Loans, net of unearned income	688,922		689,362
Corporate loans
Assets
Loans	7,804		7,281
Liabilities
Allowance for credit losses	2,591	$ 2,484	2,714	$ 2,717	$ 2,630	$ 2,855
Loans, net of unearned income	299,771		300,165
Lease financing
Liabilities
Loans, net of unearned income	300		300
Lease financing | Corporate loans
Liabilities
Loans, net of unearned income	274		275
Carrying value
Assets
HTM debt securities, net of allowance(1)	253,600		259,700
Securities borrowed and purchased under agreements to resell	138,000		139,600
Loans	662,200		663,300
Other financial assets	403,800		347,500
Liabilities
Deposits	1,305,900		1,306,200
Securities loaned and sold under agreements to repurchase	215,500		215,600
Long-term debt	181,700		170,300
Other financial liabilities	146,400		132,800
Allowance for credit losses	18,400		18,100
Estimated fair value
Assets
HTM debt securities, net of allowance(1)	239,800		240,600
Securities borrowed and purchased under agreements to resell	138,000		139,700
Loans	669,000		673,200
Other financial assets	403,800		347,500
Liabilities
Deposits	1,305,700		1,305,900
Securities loaned and sold under agreements to repurchase	215,500		215,600
Long-term debt	186,800		173,400
Other financial liabilities	146,400		132,800
Estimated fair value | Corporate loans
Liabilities
Loans, net of unearned income	7,804		7,281
Estimated fair value | Level 1
Assets
HTM debt securities, net of allowance(1)	126,500		124,000
Securities borrowed and purchased under agreements to resell	0		0
Loans	0		0
Other financial assets	284,900		243,100
Liabilities
Deposits	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)	110,900		114,100
Securities borrowed and purchased under agreements to resell	138,000		139,700
Loans	0		0
Other financial assets	18,200		17,800
Liabilities
Deposits	1,305,700		1,116,500
Securities loaned and sold under agreements to repurchase	215,500		215,600
Long-term debt	175,800		168,000
Other financial liabilities	27,900		29,200
Estimated fair value | Level 3
Assets
HTM debt securities, net of allowance(1)	2,400		2,500
Securities borrowed and purchased under agreements to resell	0		0
Loans	669,000		673,200
Other financial assets	100,700		86,600
Liabilities
Deposits	0		189,400
Securities loaned and sold under agreements to repurchase	0		0
Long-term debt	11,000		5,400
Other financial liabilities	118,500		103,600
Estimated fair value | Level 3 | Corporate loans
Fair value measurements additional disclosures
Unfunded lending commitments	$ 15,200		$ 14,200