Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total	Common Stock	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, 2017	$ 8,349	$ 2,673	$ 207	$ (6,757)	$ 12,668	$ (469)	$ 27
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	1,657	0	0	0	1,656	0	1
Other comprehensive income (loss)	114	0	0	0	0	114	0
Cash dividends	(630)	0	0	0	(630)	0
Cash dividends - Noncontrolling interest							0
Stock plans	415	(2)	4	413	0	0	0
Stock repurchase program	(400)	0	0	(400)	0	0	0
Other	39	0	0	0	(45)	0	(6)
Ending balance at Dec. 31, 2018	$ 9,544	2,671	211	(6,744)	13,739	(355)	22
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared	$ 0.72
Net income (loss)	$ (1,129)	0	0	0	(1,131)	0	2
Other comprehensive income (loss)	(8)	0	0	0	0	(8)	0
Cash dividends	(630)	0	0	0	(630)	0
Cash dividends - Noncontrolling interest							0
Stock plans	348	(2)	(67)	417	0	0	0
Stock repurchase program	(100)	0	0	(100)	0	0	0
Other	0	0	1	0	11	(1)	(11)
Ending balance at Dec. 31, 2019	$ 8,025	2,669	143	(6,427)	11,989	(362)	13
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared	$ 0.72
Net income (loss)	$ (2,942)	0	0	0	(2,945)	0	3
Other comprehensive income (loss)	0
Cash dividends	(278)	0	0	0	(278)	0
Cash dividends - Noncontrolling interest							0
Stock plans	285	(3)	(143)	506	(75)	0	0
Stock repurchase program	(100)	0	0	(100)	0	0	0
Other	(7)	0	0	0	0	0	(7)
Ending balance at Dec. 31, 2020	$ 4,983	$ 2,666	$ 0	$ (6,021)	$ 8,691	$ (362)	$ 9
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared	$ 0.315