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LOANS - Corporate Loans (Details) - USD ($) $ in Millions	3 Months Ended
LOANS - Corporate Loans (Details) - USD ($) $ in Millions	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Loans
Total loans, net of unearned income	$ 659,669		$ 667,767
Lease financing
Loans
Total loans, net of unearned income	400		500
Corporate
Loans
Total loans, net of unearned income	309,341		291,233
Unearned income	(766)		(770)
Loans sold and/or reclassified to held-for-sale	300	$ 500
Corporate \| Commercial and industrial
Loans
Total loans, net of unearned income	163,361		147,004
Corporate \| Financial institutions
Loans
Total loans, net of unearned income	75,242		71,767
Corporate \| Mortgage and real estate
Loans
Total loans, net of unearned income	22,190		20,291
Corporate \| Lease financing
Loans
Total loans, net of unearned income	426		455
Corporate \| In North America offices
Loans
Total loans, net of unearned income	138,720		134,691
Corporate \| In North America offices \| Commercial and industrial
Loans
Total loans, net of unearned income	54,063		48,364
Corporate \| In North America offices \| Financial institutions
Loans
Total loans, net of unearned income	47,930		49,804
Corporate \| In North America offices \| Mortgage and real estate
Loans
Total loans, net of unearned income	17,536		15,965
Corporate \| In North America offices \| Installment and other
Loans
Total loans, net of unearned income	18,812		20,143
Corporate \| In North America offices \| Lease financing
Loans
Total loans, net of unearned income	379		415
Corporate \| In offices outside North America
Loans
Total loans, net of unearned income	170,621		156,542
Corporate \| In offices outside North America \| Commercial and industrial
Loans
Total loans, net of unearned income	112,732		102,735
Corporate \| In offices outside North America \| Financial institutions
Loans
Total loans, net of unearned income	27,657		22,158
Corporate \| In offices outside North America \| Mortgage and real estate
Loans
Total loans, net of unearned income	4,705		4,374
Corporate \| In offices outside North America \| Installment and other
Loans
Total loans, net of unearned income	21,275		22,812
Corporate \| In offices outside North America \| Lease financing
Loans
Total loans, net of unearned income	47		40
Corporate \| In offices outside North America \| Government and official institutions
Loans
Total loans, net of unearned income	$ 4,205		$ 4,423