Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Shareholders' equity activity [Roll Forward]
Beginning Balance	$ 9,625	$ 9,544	$ 8,391	$ 8,349	$ 9,544	$ 8,349
Net income (loss)	77	152	508	47	229	555
Other comprehensive income (loss)	1	1	1	(2)	2	(1)
Cash dividends	(157)	(157)	(158)	(158)
Stock repurchase program	100
Stock plans	83	87	104	127
Other	(5)	(2)	(3)	28
Ending Balance	$ 9,524	$ 9,625	$ 8,843	$ 8,391	9,524	8,843
Common Stock, Dividends, Per Share, Declared	$ 0.18	$ 0.18	$ 0.18	$ 0.18
Common Shares
Shareholders' equity activity [Roll Forward]
Beginning Balance	$ 2,671	$ 2,671	$ 2,672	$ 2,673	2,671	2,673
Net income (loss)	0	0	0	0
Other comprehensive income (loss)	0	0	0	0
Cash dividends	0	0	0	0
Stock repurchase program	0
Stock plans	(1)	0	0	(1)
Other	0	0	0	0
Ending Balance	2,670	2,671	2,672	2,672	2,670	2,672
Paid-in Capital in Excess of Par Value
Shareholders' equity activity [Roll Forward]
Beginning Balance	224	211	222	207	211	207
Net income (loss)	0	0	0	0
Other comprehensive income (loss)	0	0	0	0
Cash dividends	0	0	0	0
Stock repurchase program	0
Stock plans	(166)	13	(97)	15
Other	0	0	0	0
Ending Balance	58	224	125	222	58	125
Treasury Stock
Shareholders' equity activity [Roll Forward]
Beginning Balance	(6,670)	(6,744)	(6,644)	(6,757)	(6,744)	(6,757)
Net income (loss)	0	0	0	0
Other comprehensive income (loss)	0	0	0	0
Cash dividends	0	0	0	0
Stock repurchase program	(100)
Stock plans	250	74	201	113
Other	0	0	0	0
Ending Balance	(6,520)	(6,670)	(6,443)	(6,644)	(6,520)	(6,443)
Retained Earnings
Shareholders' equity activity [Roll Forward]
Beginning Balance	13,734	13,739	12,586	12,668	13,739	12,668
Net income (loss)	75	152	511	46
Other comprehensive income (loss)	0	0	0	0
Cash dividends	(157)	(157)	(158)	(158)
Stock repurchase program	0
Stock plans	0	0	0	0
Other	0	0	0	30
Ending Balance	13,652	13,734	12,939	12,586	13,652	12,939
Accumulated Other Comprehensive Income (Loss)
Shareholders' equity activity [Roll Forward]
Beginning Balance	(354)	(355)	(471)	(469)	(355)	(469)
Net income (loss)	0	0	0	0
Other comprehensive income (loss)	1	1	1	(2)
Cash dividends	0	0	0	0
Stock repurchase program	0
Stock plans	0	0	0	0
Other	1	0	0	0
Ending Balance	(352)	(354)	(470)	(471)	(352)	(470)
Noncontrolling Interest in Consolidated Subsidiaries
Shareholders' equity activity [Roll Forward]
Beginning Balance	20	22	26	27	22	27
Net income (loss)	2	0	(3)	1
Other comprehensive income (loss)	0	0	0	0
Cash dividends	0	0	0	0
Stock repurchase program	0
Stock plans	0	0	0	0
Other	(6)	(2)	(3)	(2)
Ending Balance	$ 16	$ 20	$ 20	$ 26	$ 16	$ 20