Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total	Common Shares	Paid-in Capital in Excess of Par Value	Treasury Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Noncontrolling interest in Consolidated Subsidiaries
Beginning balance at Dec. 31, 2012	$ (15,790)	$ (2,682)	$ (486)	$ (4,276)	$ (17,182)	$ 309	$ (25)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	2,135	0	0	0	2,125	0	10
Other Comprehensive Income (Loss), Net of Tax	2	0	0	0	0	2	0
Treasury Stock, Value, Acquired, Cost Method	(4,356)	0	0	(4,356)	0	0	0
Cash dividends	(465)	0	0	0	(465)	0
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders							0
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures	(484)	(2)	(97)	(583)	0	0	0
Other	25	0	26	0	0	0	(1)
Ending balance at Dec. 31, 2013	(13,615)	(2,680)	(415)	(8,049)	(18,842)	307	(34)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	3,501	0	0	0	3,500	0	1
Other Comprehensive Income (Loss), Net of Tax	(92)	0	0	0	0	(92)	0
Treasury Stock, Value, Acquired, Cost Method	(800)	0	0	(800)	0	0	0
Cash dividends	(533)	0	0	0	(533)	0
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders							0
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures	(556)	(1)	(161)	(718)	0	0	0
Other	51	0	55	0	0	0	(4)
Ending balance at Dec. 31, 2014	(16,298)	(2,679)	(309)	(8,131)	(21,809)	399	(31)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(667)	0	0	0	(671)	0	4
Other Comprehensive Income (Loss), Net of Tax	36	0	0	0	0	36	0
Cash dividends	(614)	0	0	0	(614)	0
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders							0
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures	(440)	(2)	(39)	(481)	0	0	0
Other	(2)	0	4	0	0	0	(2)
Ending balance at Dec. 31, 2015	$ (15,495)	$ (2,677)	$ (274)	$ (7,650)	$ (20,524)	$ 363	$ (33)