STOCKHOLDERS' EQUITY - Dividends (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Class of Stock [Line Items]
Dividends declared per share of common stock (in usd per share)	$ 0.32	$ 0.22	$ 0.64	$ 0.44
Common stock dividends declared and paid	148,000,000	107,000,000	297,000,000	215,000,000
Preferred stock dividends declared and paid	18,000,000		33,000,000	7,000,000
Series A Preferred Stock
Class of Stock [Line Items]
Dividends declared per share of preferred stock (in usd per share)	0	0	27.50	27.50
Series B Preferred Stock
Class of Stock [Line Items]
Dividends declared per share of preferred stock (in usd per share)	30.00	0	30.00	0
Series C Preferred Stock
Class of Stock [Line Items]
Dividends declared per share of preferred stock (in usd per share)	15.94	0	31.88	0
Series D Preferred Stock
Class of Stock [Line Items]
Dividends declared per share of preferred stock (in usd per share)	15.88	0	27.70	0
Dividends Declared
Class of Stock [Line Items]
Common stock dividends declared and paid	148,000,000	107,000,000	297,000,000	215,000,000
Preferred stock dividends declared and paid	18,000,000	0	33,000,000	7,000,000
Dividends Declared | Series A Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	0	0	7,000,000	7,000,000
Dividends Declared | Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	9,000,000	0	9,000,000	0
Dividends Declared | Series C Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	4,000,000	0	9,000,000	0
Dividends Declared | Series D Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	5,000,000	0	8,000,000	0
Dividends Paid
Class of Stock [Line Items]
Common stock dividends declared and paid	148,000,000	107,000,000	297,000,000	215,000,000
Preferred stock dividends declared and paid	15,000,000	7,000,000	30,000,000	7,000,000
Dividends Paid | Series A Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	7,000,000	7,000,000	7,000,000	7,000,000
Dividends Paid | Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	0	0	11,000,000	0
Dividends Paid | Series C Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	5,000,000	0	9,000,000	0
Dividends Paid | Series D Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	$ 3,000,000	$ 0	$ 3,000,000	$ 0