Net Loss Per Common Share (Calculation Of Net Income (Loss) Per Common Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Loss Per Common Share [Abstract]
Net income (loss) attributable to Frontier common shareholders	$ (1,082)	$ (92)	$ (715)	$ (129)	$ (133)	$ (134)	$ (80)	$ (240)	$ (2,018)	$ (587)	$ (316)
Less: Dividends paid on unvested restricted stock awards									(2)	(3)	(3)
Total basic net loss attributable to Frontier common shareholders									(2,020)	(590)	(319)
Effect of loss related to dilutive stock units
Total diluted net loss attributable to Frontier common shareholders									$ (2,020)	$ (590)	$ (319)
Total weighted average shares and unvested restricted stock awards outstanding - basic (in shares)									78,409	78,142	72,787
Less: Weighted average unvested restricted stock awards (in shares)									(673)	(535)	(479)
Total weighted average shares outstanding - basic (in shares)									77,736	77,607	72,308
Basic net income (loss) per share attributable to Frontier common shareholders	$ (13.91)	$ (1.19)	$ (9.20)	$ (1.67)	$ (1.73)	$ (1.73)	$ (1.05)	$ (3.10)	$ (25.99)	$ (7.61)	$ (4.41)
Total weighted average shares outstanding - diluted (in shares)									77,736	77,607	72,308
Diluted net loss per share attributable to Frontier common shareholders	$ (13.91)	$ (1.19)	$ (9.21)	$ (1.67)	$ (1.73)	$ (1.73)	$ (1.05)	$ (3.10)	$ (25.99)	$ (7.61)	$ (4.41)