FAIR VALUE MEASUREMENT - Estimate Fair Value of Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014
Assets
Loans	$ 3,970		$ 5,005
Liabilities
Deposits	940,252		907,887
Allowance for loan losses	12,439	$ 12,304	12,626	$ 13,626	$ 14,075	$ 15,994
Lease finance receivables	1,900		2,400
Corporate
Assets
Loans	3,939		4,971
Carrying value
Assets
Investments	44,800		41,700
Federal funds sold and securities borrowed or purchased under agreements to resell	92,400		81,700
Loans	620,100		597,500
Other financial assets	214,600		186,500
Liabilities
Deposits	938,800		906,300
Federal funds purchased and securities loaned or sold under agreements to repurchase	110,200		109,700
Long-term debt	181,500		176,000
Other financial liabilities	115,300		97,600
Fair value
Assets
Investments	46,100		42,700
Federal funds sold and securities borrowed or purchased under agreements to resell	92,400		81,700
Loans	617,900		599,400
Other financial assets	214,600		186,500
Liabilities
Deposits	937,300		896,700
Federal funds purchased and securities loaned or sold under agreements to repurchase	110,200		109,700
Long-term debt	186,300		180,800
Other financial liabilities	115,300		97,600
Fair value | Level 1
Assets
Investments	1,600		3,500
Federal funds sold and securities borrowed or purchased under agreements to resell	0		0
Loans	0		0
Other financial assets	7,200		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	42,600		36,400
Federal funds sold and securities borrowed or purchased under agreements to resell	86,200		77,400
Loans	8,400		6,000
Other financial assets	148,800		126,200
Liabilities
Deposits	781,900		749,400
Federal funds purchased and securities loaned or sold under agreements to repurchase	109,600		109,400
Long-term debt	156,100		153,800
Other financial liabilities	15,700		18,000
Fair value | Level 3
Assets
Investments	1,900		2,800
Federal funds sold and securities borrowed or purchased under agreements to resell	6,200		4,300
Loans	609,500		593,400
Other financial assets	58,600		53,400
Liabilities
Deposits	155,400		147,300
Federal funds purchased and securities loaned or sold under agreements to repurchase	600		300
Long-term debt	30,200		27,000
Other financial liabilities	99,600		79,600
Fair value | Level 3 | Corporate
Fair value measurements additional disclosures
Unfunded lending commitments	$ 4,400		$ 7,000