Condensed Consolidated Statement of Equity - USD ($) shares in Millions, $ in Millions	Total	Stockholders' Equity, Total [Member]		Common Stock [Member]	6.875% Convertible Preferred Stock	Additional Paid-in Capital [Member]	Accumulated Foreign Currency Adjustment Attributable to Parent [Member]		Dividends/Distributions in Excess of Earnings [Member]
Balance, shares Period Start at Dec. 31, 2016				361
Balance, value Period Start at Dec. 31, 2016		$ 7,557		$ 4	$ 0	$ 10,938	$ (6)		$ (3,379)
Preferred Stock, Shares Outstanding Period Start at Dec. 31, 2016					0
Stock-based compensation related activity, net of forfeitures, value		53		$ 0		53	0		0
Stock-based compensation related activity, net of forfeitures, shares				1
Purchases and retirement of common stock, value		(23)		$ 0		(23)	0		0
Stock Issued During Period, Shares, New Issues				4
Stock Issued During Period, Value, New Issues		(464)		$ 0		(464)
Proceeds from Issuance of Common Stock	$ 464
Purchases and retirement of common stock, shares				0
Other comprehensive income (loss)	1	1	[1]	$ 0		0	1	[1]	0
Common stock dividends/distributions		(693)							(693)
Preferred stock dividends	0
Net income (loss)	231	231		$ 0		0	0		231
Balance, shares Period End at Jun. 30, 2017				366
Balance, value Period End at Jun. 30, 2017		7,590		$ 4	$ 0	11,432	(5)		(3,841)
Preferred Stock, Shares Outstanding Period End at Jun. 30, 2017					0
Balance, shares Period Start at Mar. 31, 2017				361
Balance, value Period Start at Mar. 31, 2017		7,363		$ 4	$ 0	10,968	(6)		(3,603)
Preferred Stock, Shares Outstanding Period Start at Mar. 31, 2017					0
Stock-based compensation related activity, net of forfeitures, value		23		$ 0		23	0		0
Stock-based compensation related activity, net of forfeitures, shares				0
Purchases and retirement of common stock, value		(1)		$ 0		(1)	0		0
Stock Issued During Period, Shares, New Issues				5
Stock Issued During Period, Value, New Issues		442		$ 0		(442)
Purchases and retirement of common stock, shares				0
Other comprehensive income (loss)	1	1	[1]	$ 0		0	1	[1]	0
Common stock dividends/distributions		(350)							(350)
Preferred stock dividends	0
Net income (loss)	$ 112	112		$ 0		0	0		112
Balance, shares Period End at Jun. 30, 2017				366
Balance, value Period End at Jun. 30, 2017		7,590		$ 4	$ 0	11,432	(5)		(3,841)
Preferred Stock, Shares Outstanding Period End at Jun. 30, 2017					0
Balance, shares Period Start at Dec. 31, 2017	406			406
Balance, value Period Start at Dec. 31, 2017	$ 12,339	12,339		$ 4	$ 0	16,844	(4)		(4,505)
Preferred Stock, Shares Outstanding Period Start at Dec. 31, 2017	2				2
Balance, shares Period End at Mar. 31, 2018				415
Balance, value Period End at Mar. 31, 2018		12,832		$ 4	$ 0	17,690	(4)		(4,858)
Preferred Stock, Shares Outstanding Period End at Mar. 31, 2018					2
Balance, shares Period Start at Dec. 31, 2017	406			406
Balance, value Period Start at Dec. 31, 2017	$ 12,339	12,339		$ 4	$ 0	16,844	(4)		(4,505)
Preferred Stock, Shares Outstanding Period Start at Dec. 31, 2017	2				2
Stock-based compensation related activity, net of forfeitures, value		60		$ 0		60	0		0
Stock-based compensation related activity, net of forfeitures, shares				1
Purchases and retirement of common stock, value		(34)		$ 0		(34)	0		0
Stock Issued During Period, Shares, New Issues				8
Stock Issued During Period, Value, New Issues		841		$ 0		(841)
Proceeds from Issuance of Common Stock	$ 841
Purchases and retirement of common stock, shares				0
Other comprehensive income (loss)	(1)	(1)		$ 0		0	(1)		0
Common stock dividends/distributions		876							876
Preferred stock dividends	(57)	(57)							(57)
Net income (loss)	$ 294	294		$ 0		0	0		294
Balance, shares Period End at Jun. 30, 2018	415			415
Balance, value Period End at Jun. 30, 2018	$ 12,566	12,566		$ 4	$ 0	17,711	(5)		(5,144)
Preferred Stock, Shares Outstanding Period End at Jun. 30, 2018	2				2
Balance, shares Period Start at Mar. 31, 2018				415
Balance, value Period Start at Mar. 31, 2018		12,832		$ 4	$ 0	17,690	(4)		(4,858)
Preferred Stock, Shares Outstanding Period Start at Mar. 31, 2018					2
Stock-based compensation related activity, net of forfeitures, value		24		$ 0		24	0		0
Stock-based compensation related activity, net of forfeitures, shares				0
Purchases and retirement of common stock, value		(1)		$ 0		(1)	0		0
Stock Issued During Period, Shares, New Issues				0
Proceeds from Issuance of Common Stock		(2)		$ 0		(2)
Purchases and retirement of common stock, shares				0
Other comprehensive income (loss)	$ (1)	(1)	[1]	$ 0		0	(1)	[1]	0
Common stock dividends/distributions		(438)							(438)
Preferred stock dividends	(28)	(28)							(28)
Net income (loss)	$ 180	180		$ 0		0	0		180
Balance, shares Period End at Jun. 30, 2018	415			415
Balance, value Period End at Jun. 30, 2018	$ 12,566	$ 12,566		$ 4	$ 0	$ 17,711	$ (5)		$ (5,144)
Preferred Stock, Shares Outstanding Period End at Jun. 30, 2018	2				2

[1] See the condensed statement of operations and other comprehensive income (loss) for the components of "other comprehensive income (loss)."