Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended									9 Months Ended
	Sep. 30, 2021		Jun. 30, 2021	Mar. 31, 2021		Sep. 30, 2020		Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Shareholders' equity activity [Roll Forward]
Beginning Balance	$ 5,429		$ 5,179	$ 4,983		$ 5,196		$ 6,843	$ 8,025	$ 4,983	$ 8,025
Net income (loss)	240		230	171		(19)		(1,681)	(1,015)	641	(2,715)
Other comprehensive income (loss)	0		2			2		9	11	2	22
Cash dividends	(41)		(40)	(40)		(40)		(40)	(158)
Stock repurchase program									(100)
Stock plans	66		61	66		66		66	82
Other	1		3	1		2		1	2
Ending Balance	$ 5,693		$ 5,429	5,179		$ 5,203		$ 5,196	$ 6,843	5,693	5,203
Common Stock, Dividends, Per Share, Declared	$ 0.045		$ 0.045			$ 0.045		$ 0.045	$ 0.18
Common Shares
Shareholders' equity activity [Roll Forward]
Beginning Balance	$ 2,666		$ 2,666	2,666		$ 2,666		$ 2,669	$ 2,669	2,666	2,669
Net income (loss)	0		0	0		0		0	0
Other comprehensive income (loss)			0			0		0	0
Cash dividends	0		0	0		0		0	0
Stock repurchase program									0
Stock plans	0		0	0		0		3	0
Other	0		0	0		0		0	0
Ending Balance	2,666		2,666	2,666		2,666		2,666	2,669	2,666	2,666
Paid-in Capital in Excess of Par Value
Shareholders' equity activity [Roll Forward]
Beginning Balance	26		34	0		125		110	143	0	143
Net income (loss)	0		0	0		0		0	0
Other comprehensive income (loss)			0			0		0	0
Cash dividends	0		0	0		0		0	0
Stock repurchase program									0
Stock plans	2		(8)	34		(102)		15	(33)
Other	0		0	0		0		0	0
Ending Balance	24		26	34		23		125	110	24	23
Treasury Stock
Shareholders' equity activity [Roll Forward]
Beginning Balance	(5,808)		(5,877)	(6,021)		(6,358)		(6,412)	(6,427)	(6,021)	(6,427)
Net income (loss)	0		0	0		0		0	0
Other comprehensive income (loss)			0			0		0	0
Cash dividends	0		0	0		0		0	0
Stock repurchase program									100
Stock plans	232		69	144		222		54	115
Other	0		0	0		0		0	0
Ending Balance	(5,576)		(5,808)	(5,877)		(6,136)		(6,358)	(6,412)	(5,576)	(6,136)
Retained Earnings
Shareholders' equity activity [Roll Forward]
Beginning Balance	8,896		8,709	8,691		9,098		10,814	11,989	8,691	11,989
Net income (loss)	236		227	170		(17)		(1,676)	(1,017)
Other comprehensive income (loss)			0			0		0	0
Cash dividends	(41)		(40)	(40)		(40)		(40)	(158)
Stock repurchase program									0
Stock plans	164	[1]	0	112	[1]	54	[2]	0	0
Other	0		0	0		0		0	0
Ending Balance	8,927		8,896	8,709		8,987		9,098	10,814	8,927	8,987
Accumulated Other Comprehensive Income (Loss)
Shareholders' equity activity [Roll Forward]
Beginning Balance	(360)		(362)	(362)		(342)		(351)	(362)	(362)	(362)
Net income (loss)	0		0	0		0		0	0
Other comprehensive income (loss)			2			2		9	11
Cash dividends	0		0	0		0		0	0
Stock repurchase program									0
Stock plans	0		0	0		0		0	0
Other	0		0	0		0		0	0
Ending Balance	(360)		(360)	(362)		(340)		(342)	(351)	(360)	(340)
Noncontrolling Interest in Consolidated Subsidiaries
Shareholders' equity activity [Roll Forward]
Beginning Balance	9		9	9		7		13	13	9	13
Net income (loss)	4		3	1		(2)		(5)	2
Other comprehensive income (loss)			0			0		0	0
Cash dividends						0
Cash dividends	0		0	0				0	0
Stock repurchase program									0
Stock plans	0		0	0		0		0	0
Other	1		3	1		2		1	2
Ending Balance	$ 12		$ 9	$ 9		$ 3		$ 7	$ 13	$ 12	$ 3

[1] In January and July of 2021, we issued common stock from treasury shares for the employee stock purchase plan and for restricted stock grants. As a result, additional paid in capital in January and July of 2021 were reduced below zero, which resulted in a reduction of retained earnings by $112 million and $164 million, respectively. Additional issuances from treasury shares could similarly impact additional paid in capital and retained earnings.

[2] In July of 2020, we issued common stock from treasury shares for the employee stock purchase plan and for restricted stock grants. As a result, additional paid in capital in July of 2020 was reduced below zero, which resulted in a reduction of retained earnings by $54 million. Additional issuances from treasury shares could similarly impact additional paid in capital and retained earnings.