Net Loss Per Common Share (Calculation Of Net Loss Per Common Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net Loss Per Common Share [Abstract]
Net loss attributable to Frontier common shareholders	$ (219)	$ (426)	$ (72)	$ (33)	$ (1,082)	$ (92)	$ (715)	$ (129)	$ (750)	$ (2,018)	$ (587)
Less: Dividends paid on unvested restricted stock awards										(2)	(3)
Total basic net loss attributable to Frontier common shareholders									(750)	(2,020)	(590)
Effect of loss related to dilutive stock units
Total diluted net loss attributable to Frontier common shareholders									$ (750)	$ (2,020)	$ (590)
Total weighted average shares and unvested restricted stock awards outstanding - basic (in shares)									91,523	78,409	78,142
Less: Weighted average unvested restricted stock awards									(1,840)	(673)	(535)
Total weighted average shares outstanding - basic									89,683	77,736	77,607
Basic net loss per share attributable to Frontier common shareholders	$ (2.12)	$ (4.11)	$ (0.92)	$ (0.44)	$ (13.91)	$ (1.19)	$ (9.20)	$ (1.67)	$ (8.37)	$ (25.99)	$ (7.61)
Total weighted average shares outstanding - diluted									89,683	77,736	77,607
Diluted net loss per share attributable to Frontier common shareholders	$ (2.12)	$ (4.11)	$ (0.92)	$ (0.44)	$ (13.91)	$ (1.19)	$ (9.21)	$ (1.67)	$ (8.37)	$ (25.99)	$ (7.61)