FAIR VALUE MEASUREMENT - Estimate Fair Value of Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Assets
Loans	$ 4,793	$ 5,005
Liabilities
Deposits	934,591	907,887
Allowance for loan losses	12,712	12,626	$ 14,598	$ 15,994
Lease finance receivables	2,000	2,400
Corporate
Assets
Loans	4,760	4,971
Carrying value
Assets
Investments	42,400	41,700
Federal funds sold and securities borrowed or purchased under agreements to resell	83,300	81,700
Loans	599,300	597,500
Other financial assets	217,200	186,500
Liabilities
Deposits	933,000	906,300
Federal funds purchased and securities loaned or sold under agreements to repurchase	119,600	109,700
Long-term debt	180,700	176,000
Other financial liabilities	103,300	97,600
Fair value
Assets
Investments	43,600	42,700
Federal funds sold and securities borrowed or purchased under agreements to resell	83,300	81,700
Loans	603,400	599,400
Other financial assets	217,200	186,500
Liabilities
Deposits	925,000	896,700
Federal funds purchased and securities loaned or sold under agreements to repurchase	119,600	109,700
Long-term debt	182,700	180,800
Other financial liabilities	103,300	97,600
Fair value | Level 1
Assets
Investments	3,500	3,500
Federal funds sold and securities borrowed or purchased under agreements to resell	0	0
Loans	0	0
Other financial assets	6,900	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	37,900	36,400
Federal funds sold and securities borrowed or purchased under agreements to resell	79,000	77,400
Loans	6,400	6,000
Other financial assets	151,400	126,200
Liabilities
Deposits	774,200	749,400
Federal funds purchased and securities loaned or sold under agreements to repurchase	119,300	109,400
Long-term debt	155,400	153,800
Other financial liabilities	18,100	18,000
Fair value | Level 3
Assets
Investments	2,200	2,800
Federal funds sold and securities borrowed or purchased under agreements to resell	4,300	4,300
Loans	597,000	593,400
Other financial assets	58,900	53,400
Liabilities
Deposits	150,800	147,300
Federal funds purchased and securities loaned or sold under agreements to repurchase	300	300
Long-term debt	27,300	27,000
Other financial liabilities	85,200	79,600
Fair value | Level 3 | Corporate
Fair value measurements additional disclosures
Unfunded lending commitments	$ 6,500	$ 7,000