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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Net Loss Per Share [Abstract]
Total basic net loss attributable to Frontier common shareholders	$ (345)	$ (426)	$ (5,749)	$ (531)
Total diluted net loss attributable to Frontier common shareholders	$ (345)	$ (426)	$ (5,749)	$ (531)
Total weighted average shares and unvested restricted stock awards outstanding - basic (in shares)	105,372	105,740	105,375	88,997
Less: Weighted average unvested restricted stock awards (in shares)	(1,237)	(2,075)	(1,344)	(1,859)
Total weighted average shares outstanding - basic (in shares)	104,135	103,665	104,031	87,138
Basic net loss per share attributable to Frontier common shareholders	$ (3.31)	$ (4.11)	$ (55.26)	$ (6.09)
Total weighted average shares outstanding - diluted (in shares)	104,135	103,665	104,031	87,138
Diluted net loss per share attributable to Frontier common shareholders	$ (3.31)	$ (4.11)	$ (55.26)	$ (6.09)