Net Earnings Per Share (Reconciliation Of Net Loss Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Successor [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total basic net income attributable to Frontier common shareholders	$ 65
Total diluted net income attributable to Frontier common shareholders	$ 65
Total weighted average shares and unvested restricted stock awards outstanding - basic (in shares)	244,433
Total weighted average shares outstanding - basic	244,433
Basic net earnings per share attributable to Frontier common shareholders	$ 0.27
Total weighted average shares outstanding - basic	244,433
Total weighted average shares outstanding - diluted	245,251
Diluted net earnings per share attributable to Frontier common shareholders	$ 0.26
Successor [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effect of dilutive awards (in shares)	818,000
Predecessor [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total basic net income attributable to Frontier common shareholders		$ 60
Total diluted net income attributable to Frontier common shareholders		$ 60
Total weighted average shares and unvested restricted stock awards outstanding - basic (in shares)		104,786
Less: Weighted average unvested restricted stock awards		(230)
Total weighted average shares outstanding - basic		104,556
Basic net earnings per share attributable to Frontier common shareholders		$ 0.57
Total weighted average shares outstanding - basic		104,556
Total weighted average shares outstanding - diluted		104,896
Diluted net earnings per share attributable to Frontier common shareholders		$ 0.57
Predecessor [Member] | Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effect of dilutive awards (in shares)		340