FAIR VALUE MEASUREMENT - Estimate Fair Value of Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020
Assets
Loans	$ 4,536		$ 6,082
Liabilities
Deposits	1,321,848		1,317,230
Purchased credit-deteriorated	15,952	$ 15,393	16,455	$ 19,238	$ 21,638	$ 24,956
Loans, net of unearned income	657,333		667,767
Corporate
Assets
Loans	4,528		6,070
Liabilities
Purchased credit-deteriorated	2,969	$ 3,025	2,415	$ 2,672	$ 3,542	$ 4,776
Loans, net of unearned income	301,728		291,233
Carrying value
Assets
Investments, net of allowance	272,700		221,900
Securities borrowed and purchased under agreements to resell	118,600		110,800
Loans	636,700		644,800
Other financial assets	398,800		351,900
Liabilities
Deposits	1,319,500		1,315,600
Securities loaned and sold under agreements to repurchase	133,900		134,600
Long-term debt	168,000		171,800
Other financial liabilities	159,000		111,100
Purchased credit-deteriorated	16,000		16,500
Estimated fair value
Assets
Investments, net of allowance	255,000		221,000
Securities borrowed and purchased under agreements to resell	118,600		110,800
Loans	641,000		659,600
Other financial assets	398,800		351,900
Liabilities
Deposits	1,318,200		1,316,200
Securities loaned and sold under agreements to repurchase	133,900		134,600
Long-term debt	165,500		184,600
Other financial liabilities	159,000		111,100
Estimated fair value | Corporate
Liabilities
Loans, net of unearned income	4,528		6,070
Estimated fair value | Level 1
Assets
Investments, net of allowance	126,700		111,800
Securities borrowed and purchased under agreements to resell	0		0
Loans	0		0
Other financial assets	266,600		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	124,900		106,400
Securities borrowed and purchased under agreements to resell	118,600		106,400
Loans	0		0
Other financial assets	17,500		19,900
Liabilities
Deposits	1,175,000		1,153,900
Securities loaned and sold under agreements to repurchase	133,900		134,500
Long-term debt	161,400		171,900
Other financial liabilities	22,400		17,000
Estimated fair value | Level 3
Assets
Investments, net of allowance	3,400		2,800
Securities borrowed and purchased under agreements to resell	0		4,400
Loans	641,000		659,600
Other financial assets	114,700		89,900
Liabilities
Deposits	143,200		162,300
Securities loaned and sold under agreements to repurchase	0		100
Long-term debt	4,100		12,700
Other financial liabilities	136,600		94,100
Estimated fair value | Level 3 | Corporate
Fair value measurements additional disclosures
Unfunded lending commitments	9,900		8,100
Lease financing
Liabilities
Loans, net of unearned income	400		500
Lease financing | Corporate
Liabilities
Loans, net of unearned income	$ 432		$ 455