INVESTMENT SECURITIES - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Pre-tax, other-than-temporary impairments on investment securities			$ 0	$ 28
Gross realized gains on available-for-sale investment securities	$ 54	$ 7	197	49
Gross realized losses	(5)	(12)	(9)	(52)
Proceeds from investment securities sales and early redemptions by issuers	659	$ 416	2,433	$ 1,283
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cost and equity method investments	$ 4,452		$ 4,452		$ 4,406