Income Taxes (Schedule of Components of Income Tax Expense (Benefit)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current [Abstract]
Federal	$ 8	$ 98	$ 55
State	(6)	10
Total current	2	108	55
Deferred [Abstract]
Federal	(126)	(34)	13
State	(41)	(44)	(20)
Total deferred	(167)	(78)	(7)
Income Tax Expense (Benefit), Total	(165)	30	48
Income taxes charged (credited) to shareholders' equity of Frontier [Abstract]
Utilization of the benefits arising from restricted stock			2
Deferred income taxes (benefits) arising from the recognition of additional pension/OPEB liability	36	(90)	132
Total income taxes charged (credited) to equity of Frontier	36	(90)	134
Total income taxes	$ (129)	$ (60)	$ 182