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
	Mar. 31, 2020	Mar. 31, 2019
Net Loss Per Share [Abstract]
Total basic net loss attributable to Frontier common shareholders	$ (186)	$ (87)
Total diluted net loss attributable to Frontier common shareholders	$ (186)	$ (87)
Total weighted average shares and unvested restricted stock awards outstanding - basic (in shares)	105,060	105,426
Less: Weighted average unvested restricted stock awards (in shares)	(697)	(1,541)
Total weighted average shares outstanding - basic (in shares)	104,363	103,885
Basic net loss per share attributable to Frontier common shareholders	$ (1.78)	$ (0.84)
Total weighted average shares outstanding - diluted (in shares)	104,363	103,885
Diluted net loss per share attributable to Frontier common shareholders	$ (1.78)	$ (0.84)