Summary Of Significant Accounting Policies - Prior Period Revision (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Balance Sheet Related Disclosures [Abstract]
Derivative Asset, Noncurrent	$ 3	$ 21
Assets	19,229	19,088
Deferred Income Tax Liabilities, Net	1,366	1,393
Retained Earnings (Accumulated Deficit)	3,478	4,042
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	11,569	12,136	$ 12,111	$ 11,279
Liabilities and Equity	19,229	19,088
Income Statement Related Disclosures [Abstract]
Derivative gain (loss), net	(281)	55	(292)
Income Tax Expense (Benefit)	61	(235)	(276)
Income (loss) before income taxes	(261)	1,008	1,251
Net income (loss) attributable to common stockholders	$ (200)	$ 773	$ 978
Basic (usd per share)	$ (1.21)	$ 4.60	$ 5.71
Diluted (usd per share)	$ (1.21)	$ 4.59	$ 5.70
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ (200)	$ 773	$ 975
Previously Reported
Balance Sheet Related Disclosures [Abstract]
Derivative Asset, Noncurrent		0
Assets		19,067
Deferred Income Tax Liabilities, Net		1,389
Retained Earnings (Accumulated Deficit)		4,025
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		12,119
Liabilities and Equity		19,067
Income Statement Related Disclosures [Abstract]
Derivative gain (loss), net		34
Income Tax Expense (Benefit)		(231)
Income (loss) before income taxes		987
Net income (loss) attributable to common stockholders		$ 756
Basic (usd per share)		$ 4.50
Diluted (usd per share)		$ 4.50
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		$ 756
Revision of Prior Period, Adjustment
Balance Sheet Related Disclosures [Abstract]
Derivative Asset, Noncurrent		21
Assets		21
Deferred Income Tax Liabilities, Net		4
Retained Earnings (Accumulated Deficit)		17
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		17
Liabilities and Equity		21
Income Statement Related Disclosures [Abstract]
Derivative gain (loss), net		21
Income Tax Expense (Benefit)		(4)
Income (loss) before income taxes		21
Net income (loss) attributable to common stockholders		$ 17
Basic (usd per share)		$ 0.10
Diluted (usd per share)		$ 0.09
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		$ 17