Net Earnings Per Share (Reconciliation Of Net Loss Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	1 Months Ended	2 Months Ended	3 Months Ended	4 Months Ended	6 Months Ended
	Apr. 30, 2021	Jun. 30, 2021	Jun. 30, 2022	Apr. 30, 2021	Jun. 30, 2022
Successor [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total basic net income attributable to Frontier common shareholders		$ 99	$ 101		$ 166
Total diluted net income attributable to Frontier common shareholders		$ 99	$ 101		$ 166
Total weighted average shares and unvested restricted stock awards outstanding - basic (in shares)		244,401	244,723		244,592
Total weighted average shares outstanding - basic		244,401	244,723		244,592
Basic net earnings per share attributable to Frontier common shareholders		$ 0.41	$ 0.41		$ 0.68
Total weighted average shares outstanding - basic		244,401	244,723		244,592
Total weighted average shares outstanding - diluted		244,401	244,723		244,831
Diluted net earnings per share attributable to Frontier common shareholders		$ 0.41	$ 0.41		$ 0.68
Successor [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effect of dilutive awards (in shares)					239
Predecessor [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total basic net income attributable to Frontier common shareholders	$ 4,481			$ 4,541
Total diluted net income attributable to Frontier common shareholders	$ 4,481			$ 4,541
Total weighted average shares and unvested restricted stock awards outstanding - basic (in shares)	104,816			104,799
Less: Weighted average unvested restricted stock awards	(154)			(215)
Total weighted average shares outstanding - basic	104,662			104,584
Basic net earnings per share attributable to Frontier common shareholders	$ 42.81			$ 43.42
Total weighted average shares outstanding - basic	104,662			104,584
Total weighted average shares outstanding - diluted	105,002			104,924
Diluted net earnings per share attributable to Frontier common shareholders	$ 42.68			$ 43.28
Predecessor [Member] | Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effect of dilutive awards (in shares)	340			340