REGULATORY MATTERS - Narrative (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($) subsidiary $ / shares	Jun. 30, 2016 USD ($) $ / shares	Jun. 30, 2018 $ / shares	Dec. 31, 2017 $ / shares	Jun. 30, 2017 USD ($) subsidiary $ / shares	Jun. 30, 2016 USD ($) $ / shares	Jun. 28, 2017 USD ($)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common share dividends	$ 71,000,000	$ 64,000,000			$ 143,000,000	$ 117,000,000
Treasury stock purchased	$ 130,000,000				260,000,000
Preferred share dividends					$ 7,000,000	$ 7,000,000
Common share dividends (in Dollars per Share) | $ / shares	$ 0.14	$ 0.12			$ 0.28	$ 0.22
Share repurchase plan, authorized amount							$ 850,000,000
Banking Subsidiaries
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Number of financial subsidiaries | subsidiary	2				2
CBNA subsidiaries
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Number of financial subsidiaries | subsidiary	2				2
Scenario, Forecast
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common share dividends (in Dollars per Share) | $ / shares			$ 0.22	$ 0.18