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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Net Loss Per Share [Abstract]
Total basic net loss attributable to Frontier common shareholders	$ (181)	$ (5,317)	$ (367)	$ (5,404)
Total diluted net loss attributable to Frontier common shareholders	$ (181)	$ (5,317)	$ (367)	$ (5,404)
Total weighted average shares and unvested restricted stock awards outstanding - basic (in shares)	104,988	105,314	105,029	105,377
Less: Weighted average unvested restricted stock awards (in shares)	(463)	(1,196)	(592)	(1,390)
Total weighted average shares outstanding - basic (in shares)	104,525	104,118	104,437	103,987
Basic net loss per share attributable to Frontier common shareholders	$ (1.73)	$ (51.07)	$ (3.51)	$ (51.97)
Total weighted average shares outstanding - diluted (in shares)	104,525	104,118	104,437	103,987
Diluted net loss per share attributable to Frontier common shareholders	$ (1.73)	$ (51.07)	$ (3.51)	$ (51.97)