Net (Loss) Earnings Per Share (Reconciliation Of Net Loss Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total basic net (loss) income attributable to Frontier common shareholders	$ (2)	$ 101	$ 1	$ 166
Total diluted net (loss) income attributable to Frontier common shareholders	$ (2)	$ 101	$ 1	$ 166
Total weighted average shares and unvested restricted stock awards outstanding - basic (in shares)	245,474	244,723	245,285	244,592
Total weighted average shares outstanding - basic	245,474	244,723	245,285	244,592
Basic net (loss) earnings per share attributable to Frontier common shareholders	$ (0.01)	$ 0.41	$ 0.00	$ 0.68
Total weighted average shares outstanding - basic	245,474	244,723	245,285	244,592
Total weighted average shares outstanding - diluted	245,474	244,723	246,517	244,831
Diluted net (loss) earnings per share attributable to Frontier common shareholders	$ (0.01)	$ 0.41	$ 0.00	$ 0.68
Performance Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effect of dilutive awards (in shares)			750
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effect of dilutive awards (in shares)			482	239