Fair Value Of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2021
Fair Value Of Financial Instruments [Abstract]
Pension Plan Assets Measured At Fair Value On Recurring Basis	Successor Fair Value Measurements at December 31, 2021 ($ in millions) Total Level 1 Level 2 Level 3 Cash and Cash Equivalents $ 39  $ 39  $ - $ - U.S. Government Obligations 62  - 62  - Corporate and Other Obligations 525  - 525  - Common Stock 496  496  - - Interest in Registered Investment Companies (1) 887  887  - - Interest in Limited Partnerships and Limited Liability Companies 165  - - 165  Total investments at fair value $ 2,174  $ 1,422  $ 587  $ 165  Common/Collective Trusts (1) 510  Interest and Dividend Receivable 5  Due from Broker for Securities Sold 28  Value of Funds Held in Insurance Co. 6  Due to Broker for Securities Purchased (68) Total Plan Assets, at Fair Value $ 2,655  Predecessor Fair Value Measurements at December 31, 2020 ($ in millions) Total Level 1 Level 2 Level 3 Cash and Cash Equivalents $ 55  $ 55  $ - $ - U.S. Government Obligations 48  - 48  - Corporate and Other Obligations 506  - 506  - Common Stock 510  510  - - Preferred Stock 3  3  - - Interest in Registered Investment Companies (1) 140  140  - - Interest in Limited Partnerships and Limited Liability Companies 166  - - 166  Total investments at fair value $ 1,428  $ 708  $ 554  $ 166  Common/Collective Trusts (1) 1,073  Interest in Registered Investment Companies (1) 32  Interest and Dividend Receivable 5  Due from Broker for Securities Sold 22  Receivable Associated with Insurance Contract 7  Due to Broker for Securities Purchased (60) Total Plan Assets, at Fair Value $ 2,507  (1)Investments that are measured at fair value using the net asset value (NAV) practical expedient have not been classified in the fair value hierarchy. The fair value of common/collective trusts are estimated using the NAV per share multiplied by the number of shares of the trust investment held as of the measurement date. Additionally, the fair value of certain assets totaling $32 million as of December 31, 2019, respectively, included in “Interest in Registered Investment Companies” were estimated using the NAV practical expedient. These balances are intended to permit reconciliation of the fair value hierarchy to the plan asset amounts presented in Note 20 - Retirement Plans.
Changes In Fair Value of Plan's Level 3 Assets	Interest in Limited Partnerships and Limited Liability Companies ($ in millions) 2021 2020 Balance at beginning of year $ 166  $ 163  Realized gains 22  14  Unrealized gains (1) 3  Purchases 1  - Sales and distributions (23) (14) Balance at end of year $ 165  $ 166
Redemption Of The Plan's Level 3 Investments	Successor Liquidation Capitalization ($ in millions) Fair Value Period Rate Interest in Limited Partnerships and Limited Liability Companies (3) MS IFHF SVP LP Cayman (1) $ 1  3 years N/A 426 E. Casino Road, LLC (2) 17  N/A 7.00% 100 Comm Drive, LLC (2) 10  N/A 7.75% 100 CTE Drive, LLC (2) 12  N/A 9.50% 6430 Oakbrook Parkway, LLC (2) 27  N/A 7.75% 8001 West Jefferson, LLC (2) 30  N/A 8.75% 1500 MacCorkle Ave SE, LLC (2) 16  N/A 8.75% 400 S. Pike Road West, LLC (2) 1  N/A 8.50% 601 N. US 131, LLC (2) 1  N/A 9.50% 9260 E. Stockton Blvd., LLC (2) 7  N/A 7.25% 120 E. Lime Street, LLC (2) 9  N/A 9.00% 610 N. Morgan Street, LLC (2) 34  N/A 8.50% Total Interest in Limited Partnerships and Limited Liability Companies $ 165  (1)The partnerships’ investment objective is to seek capital appreciation principally through investing in investment funds managed by third party investment managers who employ a variety of alternative investment strategies. These instruments are subject to certain withdrawal restrictions. The Plan is in the process of liquidating its interest in the partnerships and distributions are expected to be made over the next three years.(2)The entity invests in commercial real estate properties that are leased to Frontier. The leases are triple net, whereby Frontier is responsible for all expenses, including but not limited to, insurance, repairs and maintenance and payment of property taxes.(3)All Level 3 investments have the same redemption frequency (through the liquidation of underlying investments) and redemption notice period (none). The fair value of these properties is based on independent appraisals.
Fair Value Of Long-Term Debt	Successor Predecessor 2021 2020 Carrying Carrying ($ in millions) Amount Fair Value Amount Fair Value Total debt $ 7,777  $ 7,996  $ 16,769  $ 11,635