STOCKHOLDERS' EQUITY - Dividends (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Class of Stock [Line Items]
Dividends declared per share of common stock (in usd per share)	$ 0.36	$ 0.27	$ 1.00	$ 0.71
Common stock dividends declared and paid	$ 162	$ 129	$ 459	$ 344
Preferred stock dividends declared and paid	$ 17	$ 7	$ 50	$ 14
Series A Preferred Stock
Class of Stock [Line Items]
Dividends declared per share of preferred stock (in usd per share)	$ 27.50	$ 27.50	$ 55.00	$ 55.00
Series B Preferred Stock
Class of Stock [Line Items]
Dividends declared per share of preferred stock (in usd per share)	0	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	47.81	0
Series D Preferred Stock
Class of Stock [Line Items]
Dividends declared per share of preferred stock (in usd per share)	$ 15.88	$ 0	$ 43.57	$ 0
Dividends Declared
Class of Stock [Line Items]
Common stock dividends declared and paid	$ 162	$ 129	$ 459	$ 344
Preferred stock dividends declared and paid	17	7	50	14
Dividends Declared | Series A Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	7	7	14	14
Dividends Declared | Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	0	0	9	0
Dividends Declared | Series C Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	5	0	14	0
Dividends Declared | Series D Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	5	0	13	0
Dividends Paid
Class of Stock [Line Items]
Common stock dividends declared and paid	162	129	459	344
Preferred stock dividends declared and paid	18	0	48	7
Dividends Paid | Series A Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	0	0	7	7
Dividends Paid | Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	9	0	20	0
Dividends Paid | Series C Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	4	0	13	0
Dividends Paid | Series D Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	$ 5	$ 0	$ 8	$ 0