Income Taxes (Schedule of Components of Income Tax Expense (Benefit)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current [Abstract]
Federal	$ (4)	$ (52)	$ 8
State	5	7	(6)
Total current	1	(45)	2
Deferred [Abstract]
Federal	(1,312)	(145)	(126)
State	(72)	(60)	(41)
Total deferred	(1,384)	(205)	(167)
Income Tax Expense (Benefit), Total	(1,383)	(250)	(165)
Income taxes charged (credited) to equity of Frontier [Abstract]
Utilization of the benefits arising from restricted stock	(1)	(5)
Deferred income taxes (benefits) arising from the recognition of additional pension/OPEB liability	7	(21)	36
Total income taxes charged (credited) to equity of Frontier	6	(26)	36
Total income taxes	$ (1,377)	$ (276)	$ (129)