STOCKHOLDERS' EQUITY - Dividends (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Class of Stock [Line Items]
Dividends declared per share of common stock (in usd per share)	$ 0.39	$ 0.32	$ 0.78	$ 0.64
Common stock dividends declared and paid	$ 168	$ 148	$ 336	$ 297
Preferred stock dividends declared and paid	$ 28	$ 18	$ 50	$ 33
Series A Preferred Stock
Class of Stock [Line Items]
Dividends declared per share of preferred stock (in usd per share)	$ 13.48	$ 0	$ 40.98	$ 27.50
Series B Preferred Stock
Class of Stock [Line Items]
Dividends declared per share of preferred stock (in usd per share)	30.00	30.00	30.00	30.00
Series C Preferred Stock
Class of Stock [Line Items]
Dividends declared per share of preferred stock (in usd per share)	15.94	15.94	31.88	31.88
Series D Preferred Stock
Class of Stock [Line Items]
Dividends declared per share of preferred stock (in usd per share)	15.88	15.88	31.75	27.70
Series E Preferred Stock
Class of Stock [Line Items]
Dividends declared per share of preferred stock (in usd per share)	$ 12.50	$ 0	$ 25.00	$ 0
Dividends Declared
Class of Stock [Line Items]
Common stock dividends declared and paid	$ 168	$ 148	$ 336	$ 297
Preferred stock dividends declared and paid	28	18	50	33
Dividends Declared | Series A Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	3	0	10	7
Dividends Declared | Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	9	9	9	9
Dividends Declared | Series C Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	5	4	10	9
Dividends Declared | Series D Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	5	5	10	8
Dividends Declared | Series E Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	6	0	11	0
Dividends Paid
Class of Stock [Line Items]
Common stock dividends declared and paid	168	148	336	297
Preferred stock dividends declared and paid	22	15	45	30
Dividends Paid | Series A Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	7	7	7	7
Dividends Paid | Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	0	0	9	11
Dividends Paid | Series C Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	5	5	10	9
Dividends Paid | Series D Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	5	3	10	3
Dividends Paid | Series E Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid	$ 5	$ 0	$ 9	$ 0