Income Taxes (Schedule Of Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income (loss) before income taxes	$ (261)	$ 1,008	$ 1,251
Net loss attributable to noncontrolling interests	0	0	3
Income (loss) attributable to common stockholders before income taxes	$ (261)	$ 1,008	$ 1,254
Federal statutory income tax rate	21.00%	21.00%	21.00%
Benefit (provision) for federal income taxes at the statutory rate	$ 55	$ (212)	$ (263)
State income tax provision (net of federal tax)	(5)	(12)	(12)
Other	11	(11)	(1)
Income tax benefit (provision)	$ 61	$ (235)	$ (276)
Effective income tax rate, excluding net loss attributable to noncontrolling interests	23.00%	23.00%	22.00%