CAPITAL STOCK - Schedule of Preferred Stock (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Shares Authorized (in shares)	63,500,000	85,150,000
Shares Issued (in shares)	63,500,000	63,500,000
Shares Outstanding (in shares)	63,500,000	63,500,000
Carrying Value	$ 1,536,569	$ 1,536,569	[1]
Series D
Class of Stock [Line Items]
Shares Authorized (in shares)	0	18,400,000
Shares Issued (in shares)	0	0
Shares Outstanding (in shares)	0	0
Carrying Value	$ 0	$ 0
Contractual Rate	7.50%
Series F
Class of Stock [Line Items]
Shares Authorized (in shares)	28,800,000	28,800,000
Shares Issued (in shares)	28,800,000	28,800,000
Shares Outstanding (in shares)	28,800,000	28,800,000
Carrying Value	$ 696,910	$ 696,910
Contractual Rate	6.95%
Floating Annual Rate	4.993%
Series G
Class of Stock [Line Items]
Shares Authorized (in shares)	17,000,000	19,550,000
Shares Issued (in shares)	17,000,000	17,000,000
Shares Outstanding (in shares)	17,000,000	17,000,000
Carrying Value	$ 411,335	$ 411,335
Contractual Rate	6.50%
Floating Annual Rate	4.172%
Series I
Class of Stock [Line Items]
Shares Authorized (in shares)	17,700,000	18,400,000
Shares Issued (in shares)	17,700,000	17,700,000
Shares Outstanding (in shares)	17,700,000	17,700,000
Carrying Value	$ 428,324	$ 428,324
Contractual Rate	6.75%
Floating Annual Rate	4.989%

[1] Derived from the audited consolidated financial statements at December 31, 2020.