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, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net Loss Per Common Share [Abstract]
Net loss attributable to Frontier common shareholders	$ (162)	$ (345)	$ (5,317)	$ (87)	$ (219)	$ (426)	$ (72)	$ (33)	$ (5,911)	$ (750)	$ (2,018)
Less: Dividends paid on unvested restricted stock awards											(2)
Total basic net loss attributable to Frontier common shareholders									(5,911)	(750)	(2,020)
Total diluted net loss attributable to Frontier common shareholders									$ (5,911)	$ (750)	$ (2,020)
Total weighted average shares and unvested restricted stock awards outstanding - basic (in shares)									105,356	91,523	78,409
Less: Weighted average unvested restricted stock awards									(1,291)	(1,840)	(673)
Total weighted average shares outstanding - basic									104,065	89,683	77,736
Basic net loss per share attributable to Frontier common shareholders									$ (56.80)	$ (8.37)	$ (25.99)
Total weighted average shares outstanding - diluted									104,065	89,683	77,736
Diluted net loss per share attributable to Frontier common shareholders									$ (56.80)	$ (8.37)	$ (25.99)