CAPITAL STOCK - Schedule of Preferred Stock (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Preferred Stock, shares authorized (in shares)	85,150,000	75,950,000
Preferred stock, shares issued (in shares)	81,900,000	73,400,000
Preferred Stock, shares outstanding (in shares)	81,900,000	73,400,000
Preferred Stock, carrying value	$ 1,982,026	$ 1,778,168
Series C Preferred Stock
Class of Stock [Line Items]
Preferred Stock, shares authorized (in shares)	0	7,000,000
Preferred stock, shares issued (in shares)	0	7,000,000
Preferred Stock, shares outstanding (in shares)	0	7,000,000
Preferred Stock, carrying value	$ 0	$ 169,466
Preferred Stock, contractual rate	7.625%
Series D Preferred Stock
Class of Stock [Line Items]
Preferred Stock, shares authorized (in shares)	18,400,000	18,400,000
Preferred stock, shares issued (in shares)	18,400,000	18,400,000
Preferred Stock, shares outstanding (in shares)	18,400,000	18,400,000
Preferred Stock, carrying value	$ 445,457	$ 445,457
Preferred Stock, contractual rate	7.50%
Series H Preferred Stock
Class of Stock [Line Items]
Preferred Stock, shares authorized (in shares)	0	2,200,000
Preferred stock, shares issued (in shares)	0	2,200,000
Preferred Stock, shares outstanding (in shares)	0	2,200,000
Preferred Stock, carrying value	$ 0	$ 55,000
Preferred Stock, contractual rate	8.125%
Series F Preferred Stock
Class of Stock [Line Items]
Preferred Stock, shares authorized (in shares)	28,800,000	28,800,000
Preferred stock, shares issued (in shares)	28,800,000	28,800,000
Preferred Stock, shares outstanding (in shares)	28,800,000	28,800,000
Preferred Stock, carrying value	$ 696,910	$ 696,910
Preferred Stock, contractual rate	6.95%
Preferred Stock, floating annual rate	4.993%
Series G Preferred Stock
Class of Stock [Line Items]
Preferred Stock, shares authorized (in shares)	19,550,000	19,550,000
Preferred stock, shares issued (in shares)	17,000,000	17,000,000.0
Preferred Stock, shares outstanding (in shares)	17,000,000	17,000,000
Preferred Stock, carrying value	$ 411,335	$ 411,335
Preferred Stock, contractual rate	6.50%	6.50%
Preferred Stock, floating annual rate	4.172%
Series I Preferred Stock
Class of Stock [Line Items]
Preferred Stock, shares authorized (in shares)	18,400,000	0
Preferred stock, shares issued (in shares)	17,700,000	0
Preferred Stock, shares outstanding (in shares)	17,700,000	0
Preferred Stock, carrying value	$ 428,324	$ 0
Preferred Stock, contractual rate	6.75%
Preferred Stock, floating annual rate	4.989%