BASIS OF PRESENTATION AND ACCOUNTING CHANGES - Accounting Changes (Details) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2017 USD ($)	Jan. 01, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Jan. 01, 2016 USD ($)	Dec. 31, 2015 USD ($)
New Accounting Pronouncements or Change in Accounting Principle
Net reduction to total stockholders' equity		$ (228,622)	$ (232,690)	$ (228,622)	$ (232,690)			$ (226,143)
Reclassification from AOCI		29,891		29,891				32,381
Increase (decrease) in retained earnings		155,174		155,174				146,477
Gross up of expenses		10,171	10,404	31,154	31,296
Increase in assets		1,889,133		1,889,133				1,792,077
Increase in liabilities		1,660,511		1,660,511				1,565,934
Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle
Reclassification from AOCI										$ 15
Increase (decrease) in retained earnings										$ 15
Pro Forma | Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle
Increase (decrease) in retained earnings		200		200
Increase in assets		5,000		5,000
Increase in liabilities		5,000		5,000
Pro Forma | Accounting Standards Update 2016-16
New Accounting Pronouncements or Change in Accounting Principle
Increase in DTAs		500		500
Decrease in prepaid taxes		500		500
Early adoption | Accounting Standards Update 2017-08
New Accounting Pronouncements or Change in Accounting Principle
Net reduction to total stockholders' equity							$ 156
Retained earnings
New Accounting Pronouncements or Change in Accounting Principle
Net reduction to total stockholders' equity		(155,174)	(143,678)	(155,174)	(143,678)			(146,477)			$ (133,841)
Cumulative effect adjustment after tax	[1]							(660)			15
Retained earnings | Early adoption | Accounting Standards Update 2017-08
New Accounting Pronouncements or Change in Accounting Principle
Cumulative effect adjustment after tax							(660)
Accumulated other comprehensive income (loss)
New Accounting Pronouncements or Change in Accounting Principle
Net reduction to total stockholders' equity		$ 29,891	$ 27,193	29,891	$ 27,193	$ 29,899		32,381	$ 26,115		29,344
Cumulative effect adjustment after tax	[1]							$ 504			$ (15)
Accumulated other comprehensive income (loss) | Early adoption | Accounting Standards Update 2017-08
New Accounting Pronouncements or Change in Accounting Principle
Cumulative effect adjustment after tax							$ 504
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle
Gross up of revenues				800
Gross up of expenses				$ 800
Difference between Revenue Guidance in Effect before and after Topic 606 | Pro Forma | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle
Impact of change in revenue presentation on efficiency ratio (in basis points)				0.005

[1] See Note 1 to the Consolidated Financial Statements for additional details.