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, 2023	Mar. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total basic net income attributable to Frontier common shareholders	$ 3	$ 65
Total diluted net income attributable to Frontier common shareholders	$ 3	$ 65
Total weighted average shares and unvested restricted stock awards outstanding - basic (in shares)	245,081	244,433
Total weighted average shares outstanding - basic	245,081	244,433
Basic net earnings per share attributable to Frontier common shareholders	$ 0.01	$ 0.27
Total weighted average shares outstanding - basic	245,081	244,433
Total weighted average shares outstanding - diluted	246,425	245,251
Diluted net earnings per share attributable to Frontier common shareholders	$ 0.01	$ 0.26
Performance Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effect of dilutive awards (in shares)	769
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effect of dilutive awards (in shares)	575	818