Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Millions	Total	Cumulative Effect, Period of Adoption, Adjustment	Open Market Repurchases [Member]	Common Stock [Member]	Treasury Stock [Member]	Treasury Stock [Member] Open Market Repurchases [Member]	Common Stock Shares Outstanding [Member]	Common Stock Shares Outstanding [Member] Open Market Repurchases [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Retained Earnings [Member] Cumulative Effect, Period of Adoption, Adjustment	Total Stockholders' Equity [Member]	Total Stockholders' Equity [Member] Cumulative Effect, Period of Adoption, Adjustment	Total Stockholders' Equity [Member] Open Market Repurchases [Member]	Noncontrolling Interest [Member]
Beginning Balance, Value at Dec. 31, 2018	$ 3,547			$ 4	$ (2,961)				$ 3,145	$ 113	$ 3,218		$ 3,519			$ 28
Beginning Balance, Shares at Dec. 31, 2018				445,377,826	(197,940,553)		247,437,273
Comprehensive income (loss):
Net income (loss)	425										425		425
Other comprehensive income (loss), net of tax	(237)									(237)			(237)
Total comprehensive income (loss)	188												188
Cash dividends:
Common stock	(112)										(112)		(112)
Dividend equivalent units related to employee stock-based compensation plans	(4)										(4)		(4)
Issuance of common shares	$ 23								23				23
Issuance of common shares, Shares	5,091,044			5,091,044			5,091,044
Stock-based compensation expense	$ 20								20				20
Common stock repurchased			$ (363)			$ (363)	$ (363)								$ (363)
Common stock repurchased, Shares						(28,738,164)	(28,738,164)	(28,738,164)
Shares repurchased related to employee stock-based compensation plans	$ (31)				$ (31)								(31)
Shares repurchased related to employee stock-based compensation plans, Shares	(2,753,418)				(2,753,418)		(2,753,418)
Net activity in noncontrolling interest	$ (16)															(16)
Ending Balance, Value at Sep. 30, 2019	3,252			$ 4	$ (3,355)				3,188	(124)	3,527		3,240			12
Ending Balance, Shares at Sep. 30, 2019				450,468,870	(229,432,135)		221,036,735
Beginning Balance, Value at Jun. 30, 2019	3,312			$ 4	$ (3,222)				3,181	(80)	3,418		3,301			11
Beginning Balance, Shares at Jun. 30, 2019				450,003,173	(219,508,895)		230,494,278
Comprehensive income (loss):
Net income (loss)	145										145		145
Other comprehensive income (loss), net of tax	(44)									(44)			(44)
Total comprehensive income (loss)	101												101
Cash dividends:
Common stock	(36)										(36)		(36)
Issuance of common shares	$ 4								4				4
Issuance of common shares, Shares	465,697			465,697			465,697
Stock-based compensation expense	$ 3								3				3
Common stock repurchased			(130)			$ (130)	$ (130)								(130)
Common stock repurchased, Shares						(9,703,912)	(9,703,912)	(9,703,912)
Shares repurchased related to employee stock-based compensation plans	$ (3)				$ (3)								(3)
Shares repurchased related to employee stock-based compensation plans, Shares	(219,328)				(219,328)		(219,328)
Net activity in noncontrolling interest	$ 1															1
Ending Balance, Value at Sep. 30, 2019	3,252			$ 4	$ (3,355)				3,188	(124)	3,527		3,240			12
Ending Balance, Shares at Sep. 30, 2019				450,468,870	(229,432,135)		221,036,735
Beginning Balance, Value at Dec. 31, 2019	3,349	$ (620)		$ 4	$ (3,439)				3,198	(91)	3,664	$ (620)	3,336	$ (620)		13
Beginning Balance, Shares at Dec. 31, 2019				451,094,879	(235,658,196)		215,436,683
Accounting Standards Update Extensible List		us-gaap:AccountingStandardsUpdate201613Member										us-gaap:AccountingStandardsUpdate201613Member		us-gaap:AccountingStandardsUpdate201613Member
Comprehensive income (loss):
Net income (loss)	227										227		227
Other comprehensive income (loss), net of tax	(203)									(203)			(203)
Total comprehensive income (loss)	24												24
Cash dividends:
Common stock	(93)										(93)		(93)
Dividend equivalent units related to employee stock-based compensation plans	(3)										(3)		(3)
Issuance of common shares	$ 7								7				7
Issuance of common shares, Shares	2,393,211			2,393,211			2,393,211
Stock-based compensation expense	$ 15								15				15
Common stock repurchased			(400)			$ (400)	$ (400)								(400)
Common stock repurchased, Shares						(30,628,580)	(30,628,580)	(30,628,580)
Shares repurchased related to employee stock-based compensation plans	$ (12)				$ (12)								(12)
Shares repurchased related to employee stock-based compensation plans, Shares	(921,235)				(921,235)		(921,235)
Net activity in noncontrolling interest	$ (2)															(2)
Ending Balance, Value at Sep. 30, 2020	2,265			$ 4	$ (3,851)				3,220	(294)	3,175		2,254			11
Ending Balance, Shares at Sep. 30, 2020				453,488,090	(267,208,011)		186,280,079
Beginning Balance, Value at Jun. 30, 2020	2,126			$ 4	$ (3,786)				3,215	(317)	2,999		2,115			11
Beginning Balance, Shares at Jun. 30, 2020				453,457,122	(259,538,478)		193,918,644
Comprehensive income (loss):
Net income (loss)	207										207		207
Other comprehensive income (loss), net of tax	23									23			23
Total comprehensive income (loss)	230												230
Cash dividends:
Common stock	$ (31)										(31)		(31)
Issuance of common shares, Shares	30,968			30,968			30,968
Stock-based compensation expense	$ 5								5				5
Common stock repurchased			$ (65)			$ (65)	$ (65)								$ (65)
Common stock repurchased, Shares						(7,652,700)	(7,652,700)	(7,652,700)
Shares repurchased related to employee stock-based compensation plans, Shares	(16,833)				(16,833)		(16,833)
Ending Balance, Value at Sep. 30, 2020	$ 2,265			$ 4	$ (3,851)				$ 3,220	$ (294)	$ 3,175		$ 2,254			$ 11
Ending Balance, Shares at Sep. 30, 2020				453,488,090	(267,208,011)		186,280,079