FAIR VALUE MEASUREMENT - Estimate Fair Value of Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014
Assets
Loans	$ 4,134		$ 5,005
Liabilities
Deposits	937,852		907,887
Allowance for loan losses	12,304	$ 12,712	12,626	$ 14,075	$ 14,598	$ 15,994
Lease finance receivables	1,900		2,400
Corporate
Assets
Loans	4,102		4,971
Carrying value
Assets
Investments	41,600		41,700
Federal funds sold and securities borrowed or purchased under agreements to resell	83,900		81,700
Loans	615,100		597,500
Other financial assets	215,400		186,500
Liabilities
Deposits	936,400		906,300
Federal funds purchased and securities loaned or sold under agreements to repurchase	111,900		109,700
Long-term debt	181,500		176,000
Other financial liabilities	108,200		97,600
Fair value
Assets
Investments	43,100		42,700
Federal funds sold and securities borrowed or purchased under agreements to resell	83,900		81,700
Loans	617,500		599,400
Other financial assets	215,400		186,500
Liabilities
Deposits	935,100		896,700
Federal funds purchased and securities loaned or sold under agreements to repurchase	111,900		109,700
Long-term debt	185,100		180,800
Other financial liabilities	108,200		97,600
Fair value | Level 1
Assets
Investments	1,700		3,500
Federal funds sold and securities borrowed or purchased under agreements to resell	0		0
Loans	0		0
Other financial assets	6,500		6,900
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	37,500		36,400
Federal funds sold and securities borrowed or purchased under agreements to resell	80,800		77,400
Loans	6,800		6,000
Other financial assets	143,600		126,200
Liabilities
Deposits	784,100		749,400
Federal funds purchased and securities loaned or sold under agreements to repurchase	111,500		109,400
Long-term debt	158,600		153,800
Other financial liabilities	14,700		18,000
Fair value | Level 3
Assets
Investments	3,900		2,800
Federal funds sold and securities borrowed or purchased under agreements to resell	3,100		4,300
Loans	610,700		593,400
Other financial assets	65,300		53,400
Liabilities
Deposits	151,000		147,300
Federal funds purchased and securities loaned or sold under agreements to repurchase	400		300
Long-term debt	26,500		27,000
Other financial liabilities	93,500		79,600
Fair value | Level 3 | Corporate
Fair value measurements additional disclosures
Unfunded lending commitments	$ 6,400		$ 7,000