FAIR VALUE MEASUREMENT - Estimate Fair Value of Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021
Assets
Loans	$ 5,766		$ 5,360
Liabilities
Deposits	1,319,867		1,365,954
Allowance for credit losses	17,496	$ 17,169	16,974	$ 15,952	$ 15,393	$ 16,455
Loans, net of unearned income	660,612		657,221
Corporate
Assets
Loans	5,529		5,123
Liabilities
Allowance for credit losses	2,630	$ 2,780	2,855	$ 2,969	$ 3,025	$ 2,415
Loans, net of unearned income	286,021		289,154
Carrying value
Assets
Investments, net of allowance	267,500		274,300
Securities borrowed and purchased under agreements to resell	127,000		125,900
Loans	637,100		634,500
Other financial assets	389,000		427,100
Liabilities
Deposits	1,317,300		1,364,100
Securities loaned and sold under agreements to repurchase	197,200		131,600
Long-term debt	158,600		165,600
Other financial liabilities	136,700		142,400
Allowance for credit losses	17,500		17,000
Estimated fair value
Assets
Investments, net of allowance	243,600		249,200
Securities borrowed and purchased under agreements to resell	127,000		125,900
Loans	646,900		634,900
Other financial assets	389,000		427,100
Liabilities
Deposits	1,316,300		1,345,400
Securities loaned and sold under agreements to repurchase	197,200		131,600
Long-term debt	160,700		160,500
Other financial liabilities	136,700		142,400
Estimated fair value | Corporate
Liabilities
Loans, net of unearned income	5,529		5,123
Estimated fair value | Level 1
Assets
Investments, net of allowance	124,100		123,200
Securities borrowed and purchased under agreements to resell	0		0
Loans	0		0
Other financial assets	279,200		320,000
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
Investments, net of allowance	117,200		123,100
Securities borrowed and purchased under agreements to resell	127,000		125,900
Loans	0		0
Other financial assets	17,700		22,000
Liabilities
Deposits	1,124,600		1,159,400
Securities loaned and sold under agreements to repurchase	197,200		131,600
Long-term debt	148,900		151,100
Other financial liabilities	31,600		26,500
Estimated fair value | Level 3
Assets
Investments, net of allowance	2,300		2,900
Securities borrowed and purchased under agreements to resell	0		0
Loans	646,900		634,900
Other financial assets	92,100		85,100
Liabilities
Deposits	191,700		186,000
Securities loaned and sold under agreements to repurchase	0		0
Long-term debt	11,800		9,400
Other financial liabilities	105,100		115,900
Estimated fair value | Level 3 | Corporate
Fair value measurements additional disclosures
Unfunded lending commitments	8,100		13,700
Lease financing
Liabilities
Loans, net of unearned income	300		400
Lease financing | Corporate
Liabilities
Loans, net of unearned income	$ 273		$ 354