FAIR VALUE MEASUREMENT - Estimate Fair Value of Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015
Assets
Loans	$ 4,216		$ 3,486
Liabilities
Deposits	958,743		929,406
Allowance for loan losses	12,025	$ 12,030	12,060	$ 12,304	$ 12,712	$ 12,626
Lease finance receivables	1,800		1,900
Corporate
Assets
Loans	4,189		3,457
Carrying value
Assets
Investments	56,700		52,100
Federal funds sold and securities borrowed or purchased under agreements to resell	91,200		103,600
Loans	626,700		607,000
Other financial assets	256,000		215,200
Liabilities
Deposits	957,400		928,200
Federal funds purchased and securities loaned or sold under agreements to repurchase	109,900		108,200
Long-term debt	196,200		179,900
Other financial liabilities	124,500		115,300
Fair value
Assets
Investments	57,000		52,000
Federal funds sold and securities borrowed or purchased under agreements to resell	91,200		103,600
Loans	622,000		607,300
Other financial assets	256,500		215,900
Liabilities
Deposits	955,100		927,600
Federal funds purchased and securities loaned or sold under agreements to repurchase	109,900		108,200
Long-term debt	203,700		185,500
Other financial liabilities	124,500		115,300
Fair value | Level 1
Assets
Investments	300		800
Federal funds sold and securities borrowed or purchased under agreements to resell	0		0
Loans	0		0
Other financial assets	6,700		8,200
Liabilities
Deposits	0		0
Federal funds purchased and securities loaned or sold under agreements to repurchase	0		0
Long-term debt	0		0
Other financial liabilities	0		0
Fair value | Level 2
Assets
Investments	55,100		48,600
Federal funds sold and securities borrowed or purchased under agreements to resell	86,100		98,500
Loans	5,800		7,000
Other financial assets	179,600		153,600
Liabilities
Deposits	811,600		789,700
Federal funds purchased and securities loaned or sold under agreements to repurchase	109,900		107,800
Long-term debt	175,100		156,500
Other financial liabilities	15,400		16,200
Fair value | Level 3
Assets
Investments	1,600		2,600
Federal funds sold and securities borrowed or purchased under agreements to resell	5,100		5,100
Loans	616,200		600,300
Other financial assets	70,200		54,100
Liabilities
Deposits	143,500		137,900
Federal funds purchased and securities loaned or sold under agreements to repurchase	0		400
Long-term debt	28,600		29,000
Other financial liabilities	109,100		99,100
Fair value | Level 3 | Corporate
Fair value measurements additional disclosures
Unfunded lending commitments	$ 2,400		$ 5,200