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		30		$ 0		30	0		0
Stock-based compensation related activity, net of forfeitures, shares				1
Purchases and retirement of common stock, value		(22)		$ 0		(22)	0		0
Stock Issued During Period, Shares, New Issues				0
Stock Issued During Period, Value, New Issues				$ 0		22
Proceeds from Issuance of Common Stock	$ 22
Purchases and retirement of common stock, shares				(1)
Other comprehensive income (loss)	0	0	[1]	$ 0		0	0	[1]	0
Common stock dividends/distributions		(343)							(343)
Preferred stock dividends	0
Net income (loss)	$ 119	119		$ 0		0	0		119
Balance, shares Period End at Mar. 31, 2017				361
Balance, value Period End at Mar. 31, 2017		7,363		$ 4	$ 0	10,968	(6)		(3,603)
Preferred Stock, Shares Outstanding Period End at Mar. 31, 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
Stock-based compensation related activity, net of forfeitures, value		36		$ 0		36	0		0
Stock-based compensation related activity, net of forfeitures, shares				1
Purchases and retirement of common stock, value		(33)		$ 0		(33)	0		0
Stock Issued During Period, Shares, New Issues				8
Proceeds from Issuance of Common Stock	$ 843	843		$ 0		843
Purchases and retirement of common stock, shares				0
Other comprehensive income (loss)	0	0	[1]	$ 0		0	0	[1]	0
Common stock dividends/distributions		(439)							(439)
Preferred stock dividends	(28)	(28)							(28)
Net income (loss)	$ 114	114		$ 0		0	0		114
Balance, shares Period End at Mar. 31, 2018	415			415
Balance, value Period End at Mar. 31, 2018	$ 12,832	$ 12,832		$ 4	$ 0	$ 17,690	$ (4)		$ (4,858)
Preferred Stock, Shares Outstanding Period End at Mar. 31, 2018	2				2

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