COMMON STOCK AND PREFERRED STOCK - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended		12 Months Ended
	Aug. 25, 2017	Jan. 31, 2018	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Class of Stock [Line Items]
Common Stock, par value (in dollars per share)			$ 0.01		$ 0.01
Common Stock, shares authorized (in shares)			1,909,750,000		1,929,300,000
Common Stock, shares issued (in shares)			1,159,657,350		1,159,585,078
Common Stock, shares outstanding (in shares)			1,159,657,350		1,159,585,078
Options exercised under incentive plans (In shares)			0	0
Direct purchase and dividend reinvestment program - value raised			$ 746	$ 596
Direct purchase and dividend reinvestment program - issued shares of common stock (in shares)			70,000	56,000
Redemption of preferred stock			$ 412,500
At-the-market Sale Program
Class of Stock [Line Items]
Aggregate stock offering price		$ 1,500,000
7.625% Series C Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred Stock, shares authorized (in shares)			12,000,000		12,000,000
Preferred Stock dividend rate, percentage			7.625%	7.625%	7.625%
Preferred stock redeemed (in shares)			5,000,000
Redemption of preferred stock			$ 125,000
Preferred stock dividends paid			$ 1,000
Preferred stock, dividends paid (in dollars per share)			$ 0.196
Preferred stock, redemption price (in dollars per share)			$ 25
Preferred Stock, shares issued (in shares)			7,000,000		12,000,000
Preferred Stock, shares outstanding (in shares)			7,000,000		12,000,000
Preferred Stock, par value (in dollars per share)			$ 0.01		$ 0.01
Preferred Stock liquidation preference, per share (in dollars per share)			$ 25		$ 25.00
7.50% Series D Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred Stock, shares authorized (in shares)			18,400,000		18,400,000
Preferred Stock dividend rate, percentage			7.50%	7.50%	7.50%
Preferred stock, redemption price (in dollars per share)			$ 25
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, par value (in dollars per share)			$ 0.01		$ 0.01
Preferred Stock liquidation preference, per share (in dollars per share)			$ 25		$ 25.00
6.95% Series F Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred Stock, shares authorized (in shares)			28,800,000		28,800,000
Preferred Stock dividend rate, percentage			6.95%	6.95%	6.95%
Preferred stock, redemption price (in dollars per share)			$ 25.00
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, par value (in dollars per share)			$ 0.01		$ 0.01
Preferred Stock liquidation preference, per share (in dollars per share)			$ 25.00		$ 25.00
Number of shares issued during period (in shares)			28,800,000		28,800,000
Preferred stock, basis spread			4.993%
6.50% Series G Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred Stock, shares authorized (in shares)			19,550,000		0
Preferred Stock dividend rate, percentage			6.50%	6.50%	6.50%
Preferred stock, redemption price (in dollars per share)			$ 25.00
Preferred Stock, shares issued (in shares)			17,000,000		0
Preferred Stock, shares outstanding (in shares)			17,000,000		0
Preferred Stock liquidation preference, per share (in dollars per share)			$ 25.00
Number of shares issued during period (in shares)			17,000,000
Preferred stock, basis spread			4.172%
Proceeds from stock issuance, before discounts and offering expenses			$ 425,000
7.875% Series A Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred Stock dividend rate, percentage			7.875%	7.875%	7.875%
Preferred stock redeemed (in shares)	7,412,500
Redemption of preferred stock	$ 187,500
Preferred stock, redemption price (in dollars per share)					$ 25
7.625% Series E Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred Stock, shares authorized (in shares)			11,500,000		11,500,000
Preferred Stock dividend rate, percentage			7.625%	7.625%	7.625%
Preferred stock redeemed (in shares)			11,500,000
Redemption of preferred stock			$ 287,500
Preferred Stock, shares issued (in shares)			0		11,500,000
Preferred Stock, shares outstanding (in shares)			0		11,500,000
Preferred Stock, par value (in dollars per share)					$ 0.01
Preferred Stock liquidation preference, per share (in dollars per share)					$ 25