STOCKHOLDERS' EQUITY - Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Preferred Stock
Preferred stock, authorized (in shares)	100,000,000	100,000,000
Preferred stock, par value (in dollars per share)	$ 25	$ 25
Preferred stock, issued (in shares)	850,000	250,000
Preferred stock, issued	$ 840	$ 247
Preferred stock, outstanding (in shares)	850,000	250,000
Preferred stock, outstanding	$ 840	$ 247
Series A
Preferred Stock
Preferred stock, liquidation preference (in dollars per share)	$ 1,000
Preferred stock, issued (in shares)	250,000	250,000
Preferred stock, issued	$ 247	$ 247
Preferred stock, outstanding (in shares)	250,000	250,000
Series B
Preferred Stock
Preferred stock, liquidation preference (in dollars per share)	$ 1,000
Preferred stock, issued (in shares)	300,000
Preferred stock, issued	$ 296
Preferred stock, outstanding (in shares)	300,000
Series C
Preferred Stock
Preferred stock, liquidation preference (in dollars per share)	$ 1,000
Preferred stock, issued (in shares)	300,000
Preferred stock, issued	$ 297
Preferred stock, outstanding (in shares)	300,000