Quarterly Financial Data (Schedule Of Quarterly Financial Data) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended
Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Data [Abstract]
Revenue	$ 1,942	$ 1,997	$ 2,067	$ 2,101	$ 2,124	$ 2,126	$ 2,162	$ 2,199	$ 8,107	$ 8,611	$ 9,128
Operating income (loss)	220	26	(5,459)	339	127	(33)	367	366	(4,873)	827	(1,483)
Net loss attributable to Frontier common shareholders	$ (162)	$ (345)	$ (5,317)	$ (87)	$ (219)	$ (426)	$ (72)	$ (33)	$ (5,911)	$ (750)	$ (2,018)
Basic and diluted net loss per share attributable to Frontier common shareholders	$ (1.55)	$ (3.31)	$ (51.07)	$ (0.84)	$ (2.12)	$ (4.11)	$ (0.92)	$ (0.44)	$ (56.80)	$ (8.37)	$ (25.99)
Goodwill impairment									$ 5,725	$ 641	$ 2,748
Goodwill impairment, After-tax									5,201	$ 572
Loss on disposal of Northwest Operations									446
Loss on disposal of Northwest Operations, After-tax									$ 446

Gain (Loss) on Disposition of Business, Net Of Tax

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The amount of net income or loss for the period per each share in instances when basic and diluted earnings per share are the same amount and reported as a single line item on the face of the financial statements. Basic earnings per share is the amount of net income or loss for the period per each share of common stock or unit outstanding during the reporting period. Diluted earnings per share includes the amount of net income or loss for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Amount of gain (loss) from sale and disposal of integrated set of activities and assets capable of being conducted and managed for purpose of providing return in form of dividend, lower cost, or other economic benefit to investor, owner, member and participant.

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Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount after tax of loss recognized that results from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.

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The net result for the period of deducting operating expenses from operating revenues.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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