FAIR VALUE MEASUREMENT - Estimate Fair Value of Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2025	Jun. 30, 2025	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Dec. 31, 2023
Assets
Loans	$ 7,896		$ 8,040
Liabilities
Deposits	1,383,929		1,284,458
Investments	450,732		476,657
Allowance for credit losses	19,206	$ 19,123	18,574	$ 18,356	$ 18,216	$ 18,145
Loans, net of unearned income	733,905		694,488
Corporate loans
Assets
Loans	7,870		7,759
Liabilities
Allowance for credit losses	3,001	$ 3,023	2,556	$ 2,591	$ 2,484	$ 2,714
Loans, net of unearned income	335,277		301,386
Lease financing
Liabilities
Loans, net of unearned income	200		300
Carrying value
Assets
HTM debt securities, net of allowance(1)	202,300		247,600
Securities borrowed and purchased under agreements to resell	156,600		133,200
Loans	706,600		667,600
Other financial assets	457,700		362,200
Liabilities
Deposits	1,380,200		1,280,900
Securities loaned and sold under agreements to repurchase	147,600		205,600
Long-term debt	186,000		174,500
Other financial liabilities	155,700		137,700
Allowance for credit losses	19,200		18,600
Estimated fair value
Assets
HTM debt securities, net of allowance(1)	190,600		229,800
Securities borrowed and purchased under agreements to resell	156,600		133,200
Loans	722,800		673,500
Other financial assets	457,700		362,200
Liabilities
Deposits	1,380,200		1,280,900
Securities loaned and sold under agreements to repurchase	147,600		205,600
Long-term debt	190,700		178,000
Other financial liabilities	155,700		137,700
Estimated fair value | Corporate loans
Liabilities
Loans, net of unearned income	7,870		7,759
Estimated fair value | Level 1
Assets
HTM debt securities, net of allowance(1)	89,800		120,200
Securities borrowed and purchased under agreements to resell	0		0
Loans	0		0
Other financial assets	348,100		260,600
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)	98,600		107,400
Securities borrowed and purchased under agreements to resell	156,600		133,200
Loans	0		0
Other financial assets	109,600		15,900
Liabilities
Deposits	1,380,200		1,280,900
Securities loaned and sold under agreements to repurchase	147,600		205,600
Long-term debt	186,300		162,100
Other financial liabilities	155,700		34,700
Estimated fair value | Level 3
Assets
HTM debt securities, net of allowance(1)	2,200		2,200
Securities borrowed and purchased under agreements to resell	0		0
Loans	722,800		673,500
Other financial assets	0		85,700
Liabilities
Deposits	0		0
Securities loaned and sold under agreements to repurchase	0		0
Long-term debt	4,400		15,900
Other financial liabilities	0		103,000
Estimated fair value | Level 3 | Corporate loans
Fair value measurements additional disclosures
Unfunded lending commitments	10,700		13,500
Carried at cost | Non-marketable equity securities
Liabilities
Investments	$ 5,200		$ 5,200