Condensed Consolidated Statement of Equity - USD ($) shares in Millions, $ in Millions		Total		Common Stock [Member]	6.875% Mandatory Convertible Preferred Stock [Member]	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		75		$ 0		75	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				44	2
Proceeds from Issuance of Convertible Preferred Stock		1,608				1,608
Stock Issued During Period, Value, New Issues		4,221		$ 0		4,221
Proceeds from Issuance of Common Stock		4,221
Purchases and retirement of common stock, shares				0
Other comprehensive income (loss)		1	[1]	$ 0		0	1	[1]	0
Common stock dividends/distributions		(1,083)							(1,083)
Preferred stock dividends		(30)							(30)
Net income (loss)		346		$ 0		0	0		346
Balance, shares Period End at Sep. 30, 2017				406
Balance, value Period End at Sep. 30, 2017		12,672		$ 4	$ 0	16,819	(5)		(4,146)
Preferred Stock, Shares Outstanding Period End at Sep. 30, 2017					2
Balance, shares Period Start at Jun. 30, 2017				366
Balance, value Period Start at Jun. 30, 2017		7,591		$ 4	$ 0	11,433	(5)		(3,841)
Preferred Stock, Shares Outstanding Period Start at Jun. 30, 2017					0
Stock-based compensation related activity, net of forfeitures, value		22				22
Stock-based compensation related activity, net of forfeitures, shares				0
Purchases and retirement of common stock, value		0				0
Stock Issued During Period, Shares, New Issues				40	2
Proceeds from Issuance of Convertible Preferred Stock		1,608				1,608
Stock Issued During Period, Value, New Issues		3,756				3,756
Purchases and retirement of common stock, shares				0
Other comprehensive income (loss)	[1]	0
Common stock dividends/distributions		(390)							(390)
Preferred stock dividends		(30)							(30)
Net income (loss)		115							115
Balance, shares Period End at Sep. 30, 2017				406
Balance, value Period End at Sep. 30, 2017		$ 12,672		$ 4	$ 0	16,819	(5)		(4,146)
Preferred Stock, Shares Outstanding Period End at Sep. 30, 2017					2
Balance, shares Period Start at Dec. 31, 2017		406		406
Balance, value Period Start at Dec. 31, 2017		$ 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		$ 92		$ 0		92	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
Proceeds from Issuance of Convertible Preferred Stock		0
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)	[1]	0
Common stock dividends/distributions		(1,315)							(1,315)
Preferred stock dividends		(85)							(85)
Net income (loss)		$ 458		$ 0		0	0		458
Balance, shares Period End at Sep. 30, 2018		415		415
Balance, value Period End at Sep. 30, 2018		$ 12,295		$ 4	$ 0	17,743	(5)		(5,447)
Preferred Stock, Shares Outstanding Period End at Sep. 30, 2018		2			2
Balance, shares Period Start at Jun. 30, 2018				415
Balance, value Period Start at Jun. 30, 2018		$ 12,566		$ 4	$ 0	17,711	(5)		(5,144)
Preferred Stock, Shares Outstanding Period Start at Jun. 30, 2018					2
Stock-based compensation related activity, net of forfeitures, value		32				32
Stock-based compensation related activity, net of forfeitures, shares				0
Purchases and retirement of common stock, value		(1)				(1)
Stock Issued During Period, Shares, New Issues				0
Stock Issued During Period, Value, New Issues		1				1
Purchases and retirement of common stock, shares				0
Other comprehensive income (loss)	[1]	0
Common stock dividends/distributions		(439)							(439)
Preferred stock dividends		(28)							(28)
Net income (loss)		$ 164							164
Balance, shares Period End at Sep. 30, 2018		415		415
Balance, value Period End at Sep. 30, 2018		$ 12,295		$ 4	$ 0	$ 17,743	$ (5)		$ (5,447)
Preferred Stock, Shares Outstanding Period End at Sep. 30, 2018		2			2

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