Net Loss Per Share (Calculation Of Net Income (Loss) Per Common Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net Loss Per Share [Abstract]
Net loss attributable to Frontier common shareholders	$ (426)	$ (92)	$ (531)	$ (936)
Less: Dividends paid on unvested restricted stock awards				(2)
Total basic net loss attributable to Frontier common shareholders	(426)	(92)	(531)	(938)
Effect of loss related to dilutive stock units				(2)
Total diluted net loss attributable to Frontier common shareholders	$ (426)	$ (92)	$ (531)	$ (940)
Total weighted average shares and unvested restricted stock awards outstanding - basic (in shares)	105,740	78,488	88,997	78,399
Less: Weighted average unvested restricted stock awards (in shares)	(2,075)	(691)	(1,859)	(685)
Total weighted average shares outstanding - basic (in shares)	103,665	77,797	87,138	77,714
Basic net loss per share attributable to Frontier common shareholders	$ (4.11)	$ (1.19)	$ (6.09)	$ (12.06)
Effect of dilutive stock units (in shares)				161
Total weighted average shares outstanding - diluted (in shares)	103,665	77,797	87,138	77,875
Diluted net loss per share attributable to Frontier common shareholders	$ (4.11)	$ (1.19)	$ (6.09)	$ (12.07)