FAIR VALUE MEASUREMENT - Estimate Fair Value of Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013
Assets
Loans	$ 5,513		$ 5,901
Liabilities
Deposits	904,243		899,332
Allowance for loan losses	13,626	$ 14,075	15,994	$ 16,915	$ 17,890	$ 19,648
Lease finance receivables	2,400		2,700
Corporate
Assets
Loans	5,476		5,858
Carrying value
Assets
Investments	39,500		30,500
Federal funds sold and securities borrowed or purchased under agreements to resell	88,200		98,400
Loans	600,900		620,000
Other financial assets	222,500		213,800
Liabilities
Deposits	902,500		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	129,200		136,700
Long-term debt	187,300		196,900
Other financial liabilities	108,100		136,200
Fair value
Assets
Investments	40,700		32,200
Federal funds sold and securities borrowed or purchased under agreements to resell	88,200		98,400
Loans	598,800		617,600
Other financial assets	222,500		213,800
Liabilities
Deposits	926,600		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	129,200		136,700
Long-term debt	191,700		202,500
Other financial liabilities	108,100		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	7,800		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	34,300		25,200
Federal funds sold and securities borrowed or purchased under agreements to resell	81,400		89,700
Loans	7,000		5,600
Other financial assets	151,900		151,900
Liabilities
Deposits	781,400		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	128,800		136,500
Long-term debt	166,800		172,700
Other financial liabilities	19,100		41,400
Fair value | Level 3
Assets
Investments	2,700		2,500
Federal funds sold and securities borrowed or purchased under agreements to resell	6,800		8,700
Loans	591,800		612,000
Other financial assets	62,800		53,600
Liabilities
Deposits	145,200		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	400		200
Long-term debt	24,900		29,800
Other financial liabilities	89,000		94,800
Fair value | Level 3 | Corporate
Fair value measurements additional disclosures
Unfunded lending commitments	$ 4,700		$ 5,500