FAIR VALUE MEASUREMENT - Estimate Fair Value of Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013
Assets
Loans	$ 6,538		$ 5,901
Liabilities
Deposits	908,037		899,332
Allowance for loan losses	14,075	$ 14,598	15,994	$ 17,890	$ 18,923	$ 19,648
Lease finance receivables	2,500		2,700
Corporate
Assets
Loans	6,499		5,858
Carrying value
Assets
Investments	35,700		30,500
Federal funds sold and securities borrowed or purchased under agreements to resell	105,000		98,400
Loans	609,000		620,000
Other financial assets	225,300		213,800
Liabilities
Deposits	906,600		897,600
Federal funds purchased and securities loaned or sold under agreements to repurchase, selected portfolios of securities sold under agreements to repurchase and securities loaned	138,300		136,700
Long-term debt	184,600		196,900
Other financial liabilities	110,500		136,200
Fair value
Assets
Investments	36,800		32,200
Federal funds sold and securities borrowed or purchased under agreements to resell	105,000		98,400
Loans	607,400		617,600
Other financial assets	225,300		213,800
Liabilities
Deposits	926,400		894,400
Federal funds purchased and securities loaned or sold under agreements to repurchase, selected portfolios of securities sold under agreements to repurchase and securities loaned	138,300		136,700
Long-term debt	190,400		202,500
Other financial liabilities	110,500		136,200
Fair value | Level 1
Assets
Investments	3,700		4,500
Federal funds sold and securities borrowed or purchased under agreements to resell	0		0
Loans	0		0
Other financial assets	8,200		8,300
Liabilities
Deposits	0		0
Federal funds purchased and securities loaned or sold under agreements to repurchase, selected portfolios of securities sold under agreements to repurchase and securities loaned	0		0
Long-term debt	0		0
Other financial liabilities	0		0
Fair value | Level 2
Assets
Investments	30,500		25,200
Federal funds sold and securities borrowed or purchased under agreements to resell	97,100		89,700
Loans	6,900		5,600
Other financial assets	145,900		151,900
Liabilities
Deposits	769,200		766,700
Federal funds purchased and securities loaned or sold under agreements to repurchase, selected portfolios of securities sold under agreements to repurchase and securities loaned	137,800		136,500
Long-term debt	169,500		172,700
Other financial liabilities	20,800		41,400
Fair value | Level 3
Assets
Investments	2,600		2,500
Federal funds sold and securities borrowed or purchased under agreements to resell	7,900		8,700
Loans	600,500		612,000
Other financial assets	71,200		53,600
Liabilities
Deposits	157,200		127,700
Federal funds purchased and securities loaned or sold under agreements to repurchase, selected portfolios of securities sold under agreements to repurchase and securities loaned	500		200
Long-term debt	20,900		29,800
Other financial liabilities	89,700		94,800
Fair value | Level 3 | Corporate
Fair value measurements additional disclosures
Unfunded lending commitments	$ 4,600		$ 5,500