FAIR VALUE MEASUREMENT - Estimate Fair Value of Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Assets
Loans	$ 4,035	$ 3,486
Liabilities
Deposits	949,990	929,406
Allowance for loan losses	12,030	12,060	$ 12,712	$ 12,626
Lease finance receivables	1,800	1,900
Corporate
Assets
Loans	4,007	3,457
Carrying value
Assets
Investments	54,000	52,100
Federal funds sold and securities borrowed or purchased under agreements to resell	105,600	103,600
Loans	610,700	607,000
Other financial assets	242,300	215,200
Liabilities
Deposits	948,700	928,200
Federal funds purchased and securities loaned or sold under agreements to repurchase	107,300	108,200
Long-term debt	181,000	179,900
Other financial liabilities	110,200	115,300
Fair value
Assets
Investments	53,900	52,000
Federal funds sold and securities borrowed or purchased under agreements to resell	105,600	103,600
Loans	604,000	604,500
Other financial assets	242,800	215,900
Liabilities
Deposits	947,100	927,600
Federal funds purchased and securities loaned or sold under agreements to repurchase	107,300	108,200
Long-term debt	187,500	185,500
Other financial liabilities	110,200	115,300
Fair value | Level 1
Assets
Investments	900	800
Federal funds sold and securities borrowed or purchased under agreements to resell	0	0
Loans	0	0
Other financial assets	7,000	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	50,500	48,600
Federal funds sold and securities borrowed or purchased under agreements to resell	100,600	98,500
Loans	7,300	7,000
Other financial assets	173,200	153,600
Liabilities
Deposits	800,500	789,700
Federal funds purchased and securities loaned or sold under agreements to repurchase	107,200	107,800
Long-term debt	158,700	156,500
Other financial liabilities	14,900	16,200
Fair value | Level 3
Assets
Investments	2,500	2,600
Federal funds sold and securities borrowed or purchased under agreements to resell	5,000	5,100
Loans	596,700	597,500
Other financial assets	62,600	54,100
Liabilities
Deposits	146,600	137,900
Federal funds purchased and securities loaned or sold under agreements to repurchase	100	400
Long-term debt	28,800	29,000
Other financial liabilities	95,300	99,100
Fair value | Level 3 | Corporate
Fair value measurements additional disclosures
Unfunded lending commitments	$ 2,900	$ 5,200