Income Taxes (Schedule Of Components Of Income Tax Expense (Benefit)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current [Abstract]
Federal	$ 1	$ (1)	$ (4)
State	7	6	5
Total Current	8	5	1
Deferred [Abstract]
Federal	(606)	(77)	(1,312)
State	(13)	10	(72)
Total Deferred	(619)	(67)	(1,384)
Total income tax benefit	(611)	(62)	(1,383)
Income taxes charged (credited) to equity of Frontier [Abstract]
Utilization of the benefits arising from restricted stock			(1)
Deferred income taxes (benefits) arising from the recognition of additional pension/OPEB liability	32	(31)	7
Total income taxes charged (credited) to equity of Frontier	32	(31)	6
Total income tax benefit	$ (579)	$ (93)	$ (1,377)