FAIR VALUE MEASUREMENT - Estimate Fair Value of Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020
Assets
Loans	$ 3,879		$ 6,082
Liabilities
Deposits	1,306,486		1,317,230
Purchased credit-deteriorated	16,309	$ 15,952	16,455	$ 17,715	$ 19,238	$ 24,956
Loans, net of unearned income	645,960		667,767
Corporate
Assets
Loans	3,638		6,070
Liabilities
Purchased credit-deteriorated	2,948	$ 2,969	2,415	$ 2,610	$ 2,672	$ 4,776
Loans, net of unearned income	288,377		291,233
Carrying value
Assets
Investments, net of allowance	273,300		221,900
Securities borrowed and purchased under agreements to resell	120,200		110,800
Loans	625,500		644,800
Other financial assets	410,900		351,900
Liabilities
Deposits	1,304,000		1,315,600
Securities loaned and sold under agreements to repurchase	130,300		134,600
Long-term debt	161,200		171,800
Other financial liabilities	157,300		111,100
Purchased credit-deteriorated	16,300		16,500
Estimated fair value
Assets
Investments, net of allowance	245,400		221,000
Securities borrowed and purchased under agreements to resell	120,300		110,800
Loans	627,200		659,600
Other financial assets	410,900		351,900
Liabilities
Deposits	1,299,400		1,316,200
Securities loaned and sold under agreements to repurchase	130,300		134,600
Long-term debt	154,000		184,600
Other financial liabilities	157,300		111,100
Estimated fair value | Corporate
Liabilities
Loans, net of unearned income	3,638		6,070
Estimated fair value | Level 1
Assets
Investments, net of allowance	122,200		111,800
Securities borrowed and purchased under agreements to resell	0		0
Loans	0		0
Other financial assets	281,000		242,100
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
Investments, net of allowance	120,100		106,400
Securities borrowed and purchased under agreements to resell	120,300		106,400
Loans	0		0
Other financial assets	18,600		19,900
Liabilities
Deposits	1,139,500		1,153,900
Securities loaned and sold under agreements to repurchase	130,300		134,500
Long-term debt	117,200		171,900
Other financial liabilities	26,400		17,000
Estimated fair value | Level 3
Assets
Investments, net of allowance	3,100		2,800
Securities borrowed and purchased under agreements to resell	0		4,400
Loans	627,200		659,600
Other financial assets	111,300		89,900
Liabilities
Deposits	159,900		162,300
Securities loaned and sold under agreements to repurchase	0		100
Long-term debt	36,800		12,700
Other financial liabilities	130,900		94,100
Estimated fair value | Level 3 | Corporate
Fair value measurements additional disclosures
Unfunded lending commitments	11,300		8,100
Lease financing
Liabilities
Loans, net of unearned income	400		500
Lease financing | Corporate
Liabilities
Loans, net of unearned income	$ 431		$ 455