Quarterly Financial Data (Schedule Of Quarterly Financial Data) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Data [Abstract]
Revenue	$ 1,695	$ 1,726	$ 1,801	$ 1,933	$ 1,942	$ 1,997	$ 2,067	$ 2,101	$ 7,155	$ 8,107	$ 8,611
Operating income	277	270	140	272	221	26	(5,459)	339	959	(4,873)	827
Net earnings (loss) attributable to Frontier common shareholders	$ (50)	$ 15	$ (181)	$ (186)	$ (162)	$ (345)	$ (5,317)	$ (87)	$ (402)	$ (5,911)	$ (750)
Basic and diluted net earnings (loss) per share attributable to Frontier common shareholders	$ (0.48)	$ 0.14	$ (1.73)	$ (1.78)	$ (1.55)	$ (3.31)	$ (51.07)	$ (0.84)	$ (3.85)	$ (56.80)	$ (8.37)
Reorganization items, net									$ 409
Reorganization items, net of tax									361
Goodwill impairment										5,725	$ 641
Goodwill impairment, After-tax										5,201
Loss on disposal of Northwest Operations									162	446
Loss on disposal of Northwest Operations, After-tax									$ 118	$ 446