Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Total
Balance at Dec. 31, 2014	$ 178	$ (8,528)	$ 7,599	$ 36,067	$ (357)	$ 34,959
Increase (Decrease) in Stockholders' Equity
Net income (loss)				(7,829)		(7,829)
Other comprehensive income (loss), net of tax					50	50
Dividends on common stock				(2,278)		(2,278)
Issuance of common stock and other, net			41			41
Purchases of treasury stock		(593)				(593)
Balance at Dec. 31, 2015	178	(9,121)	7,640	25,960	(307)	24,350
Increase (Decrease) in Stockholders' Equity
Net income (loss)				(574)		(574)
Other comprehensive income (loss), net of tax					41	41
Dividends on common stock				(2,405)		(2,405)
Issuance of common stock and other, net			107			107
Purchases of treasury stock		(22)				(22)
Balance at Dec. 31, 2016	178	(9,143)	7,747	22,981	(266)	21,497
Increase (Decrease) in Stockholders' Equity
Net income (loss)				1,311		1,311
Other comprehensive income (loss), net of tax					8	8
Dividends on common stock				(2,357)		(2,357)
Issuance of common stock and other, net	1		137			138
Purchases of treasury stock		(25)				(25)
Balance at Dec. 31, 2017	$ 179	$ (9,168)	$ 7,884	$ 21,935	$ (258)	$ 20,572