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Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Income Taxes Income Tax Disclosure [Text Block] Other (Note 16) Total Other Noncash Income (Expense) Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Consideration transferred Total consideration Business Combination, Consideration Transferred Entity Filer Category Entity Filer Category Fair Value Debt Securities, Available-for-Sale, Unrealized Loss Position Supplemental Cash Flow Elements [Abstract] Non-cash investing activities Noncash Investing And Operating Activities [Abstract] Noncash Investing And Operating Activities Asset Retirement Obligation [Line Items] Asset Retirement Obligation [Line Items] Asset Retirement Obligation [Line Items] Schedule of Effect of Netting, Offsetting Liabilities Offsetting Liabilities [Table Text Block] Postretirement benefit obligations (Note 12) Postemployment Benefits Liability, Noncurrent Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Retirement of treasury stock Treasury Stock, Retired, Cost Method, Amount TLB-2 TLB-2 Facility [Member] TLB-2 Facility Investments, Debt and Equity Securities [Abstract] Fixed-cost monthly payments Fixed-Cost Annual Payments Fixed-Cost Annual Payments Net Income (Loss) Net Income (Loss) Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Closing price of TEC common stock (in usd per share) Business Combination, Price Per Share Operating Revenues Business Combination, Pro Forma Information, Pro Forma Revenue Derivative liabilities, total Derivative Liability Equity securities, Unrealized Losses Equity Securities, FV-NI, Accumulated Gross Unrealized Loss, Before Tax Equity Securities, FV-NI, Accumulated Gross Unrealized Loss, Before Tax Entity Address, Address Line One Entity Address, Address Line One Vested (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Income tax benefit (expense) (Note 4) Income tax benefit (expense) Income Tax Expense (Benefit) Non-cash reconciliation adjustments: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Noncash Item [Abstract] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Principles of Consolidation Consolidation, Policy [Policy Text Block] Total asset retirement obligations and accrued environmental costs Asset Retirement Obligation And Accrued Environmental Costs Asset Retirement Obligation And Accrued Environmental Costs Deferred income taxes Business Combination, Recognized Liability Assumed, Deferred Tax Liability Statement [Table] Statement [Table] Unrealized Gains Decommissioning Fund Investments, Accumulated Gross Unrealized Gain, Before Tax Decommissioning Fund Investments, Accumulated Gross Unrealized Gain, Before Tax Schedule of Future Performance Obligations Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table Text Block] Derivative Instruments and Hedging Activities Disclosures [Line Items] Derivative Instruments and Hedging Activities Disclosures [Line Items] Fed Funds Effective Rate Overnight Index Swap Rate Fed Funds Effective Rate Overnight Index Swap Rate [Member] Assets, Gross Derivative Instruments Derivative Asset, Subject to Master Netting Arrangement, before Offset Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Axis] Share retirements (in shares) Treasury Stock, Shares, Retired Derivative Instruments and Hedging Activities Disclosure [Abstract] UNITED STATES