Net Earnings Per Share (Reconciliation Of Net Loss Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	4 Months Ended	8 Months Ended	12 Months Ended
	Apr. 30, 2021	Dec. 31, 2021	Dec. 31, 2022	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Net income (loss) attributable to Frontier common shareholders	$ 4,541	$ 414	$ 441	$ (402)
Total basic net income attributable to Frontier common shareholders	4,541	414	441	(402)
Total diluted net income attributable to Frontier common shareholders	$ 4,541	$ 414	$ 441	$ (402)
Total weighted average shares and unvested restricted stock awards outstanding - basic (in shares)	104,799	244,405	244,781	104,944
Less: Weighted average unvested restricted stock awards	(215)			(477)
Total weighted average shares outstanding - basic	104,584	244,405	244,781	104,467
Basic net earnings (loss) per share attributable to Frontier common shareholders	$ 43.42	$ 1.69	$ 1.80	$ (3.85)
Total weighted average shares outstanding - basic	104,584	244,405	244,781	104,467
Total weighted average shares outstanding - diluted	104,924	245,885	245,280	104,467
Diluted net earnings (loss) per share attributable to Frontier common shareholders	$ 43.28	$ 1.68	$ 1.80	$ (3.85)
Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effect of dilutive awards (in shares)	340	1,480
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effect of dilutive awards (in shares)			499