Income Taxes (Schedule of Components of Income Tax Expense (Benefit)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current [Abstract]
Federal	$ (52)	$ 8	$ 98
State	7	(6)	10
Total current	(45)	2	108
Deferred [Abstract]
Federal	(145)	(126)	(34)
State	(60)	(41)	(44)
Total deferred	(205)	(167)	(78)
Income Tax Expense (Benefit), Total	(250)	(165)	30
Income taxes charged (credited) to shareholders' equity of Frontier [Abstract]
Utilization of the benefits arising from restricted stock	(5)
Deferred income taxes (benefits) arising from the recognition of additional pension/OPEB liability	(21)	36	(90)
Total income taxes charged (credited) to equity of Frontier	(26)	36	(90)
Total income taxes	$ (276)	$ (129)	$ (60)