Long-Term Debt (Long-Term Debt) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2025	Dec. 31, 2024
Debt Instrument [Line Items]
Principal debt outstanding, beginning	$ 11,569
New Borrowings	100
Principal debt outstanding, ending	11,669
Less: Debt issuance costs	(101)	$ (89)
Less: Current portion	(10)	(10)
Less: Debt premium / (discount)	(41)	(44)
Plus: Unamortized fair value adjustments	116	125
Long-term debt	11,633	$ 11,551
Long-term debt, fair value adjustment	236
Secured Debt Issued By Frontier [Member]
Debt Instrument [Line Items]
Principal debt outstanding, beginning	8,436
Principal debt outstanding, ending	8,436
Secured Debt Issued By Subsidiaries [Member]
Debt Instrument [Line Items]
Principal debt outstanding, beginning	2,383
New Borrowings	100
Principal debt outstanding, ending	2,483
Unsecured Debt Issued By Subsidiaries [Member]
Debt Instrument [Line Items]
Principal debt outstanding, beginning	750
Principal debt outstanding, ending	$ 750

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Long Term Debt Fair Value Adjustment

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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