STOCKHOLDERS' EQUITY (Details) - USD ($) $ / shares in Units, $ in Millions		6 Months Ended		12 Months Ended
	May 24, 2018	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Preferred Stock
Preferred stock, authorized (in shares)		100,000,000		100,000,000
Preferred stock, outstanding (in shares)		550,000		250,000
Preferred stock, par value (in dollars per share)		$ 25.00		$ 25.00
Preferred stock, shares issued (in shares)		550,000		250,000
Preferred stock, carrying amount		$ 543		$ 247
Preferred stock issued		296
Treasury Stock
Treasury stock purchased		$ 325	$ 260
Treasury stock purchased (in shares)		7,486,165
Noncumulative Preferred Stock
Preferred Stock
Preferred stock, par value (in dollars per share)	$ 25
Preferred stock issued	$ 300
Preferred stock issued (in shares)	300,000
Preferred stock, dividend rate	6.00%
Preferred stock, liquidation preference per share (in dollars per share)	$ 1,000
Preferred stock, redemption notice period	90 days
Preferred stock, redemption price per share (in dollars per share)	$ 1,000
Carrying amount of preferred stock	$ 296
Series A Preferred Stock
Preferred Stock
Preferred stock, shares issued (in shares)		250,000		250,000
Preferred stock, dividend rate		5.50%		5.50%
Preferred stock, liquidation preference per share (in dollars per share)		$ 1,000		$ 1,000
Carrying amount of preferred stock		$ 247		$ 247
LIBOR | Noncumulative Preferred Stock
Preferred Stock
Preferred stock, dividend payment rate, basis spread on variable rate	3.003%