| **Income Taxes (Narrative) (Details) - USD ($)**                         | 12 Months Ended |
|--------------------------------------------------------------------------|-----------------|
||
| **Income Taxes [Line Items]**                                            |            |   |   |
| Statutory federal tax rate                                               | 21.00%          | 35.00% | 35.00% |
| Net income tax benefits                                                  | $ 64,183,000    | $ 84,766,000 | $ 78,530,000 |
| Additional net income tax benefits                                       |            | $ 3,141,000 |   |
| Percentage of catch-up bonus amortized                                   | 10.00%          |   |   |
| Catch-up adjustment                                                      | $ 38,000,000    |   |   |
| Catch-up adjustment, impact on net income                                | 16,734,000      |   |   |
| Tax deduction for qualifying capital expenditures                        | $ 380,000,000   |   |   |
| Effective income tax rate                                                | (7.70%)         | 6.60% | 8.20% |
| Expected tax refund                                                      | $ 4,593,000     |   |   |
| Regulatory assets                                                        | 788,076,000     | $ 713,971,000 |   |
| Regulatory liabilities                                                   | 531,027,000     | 541,910,000 |   |
| Unrecognized tax benefits                                                | 17,792,000      | 17,583,000 | $ 28,099,000 |
| Deferred income tax liabilities                                          | 845,403,000     | 769,073,000 |   |
| Federal [Member]                                                         |            |   |   |
| **Income Taxes [Line Items]**                                            |            |   |   |
| Operating loss carryforwards                                             | 10,835,000      |   |   |
| Operating loss carryforwards, valuation allowance                        | 0               |   |   |
| Operating loss carryforwards before unrecognized tax position            | $ 79,882,000    |   |   |
| Operating loss carryforwards, expiration beginning dates                 | Dec. 31,  2032  |   |   |
| Unrecognized tax benefits                                                | $ 69,047,000    |   |   |
| State [Member]                                                           |            |   |   |
| **Income Taxes [Line Items]**                                            |            |   |   |
| Deferred tax assets operating loss carryforward                          | 650,286,000     |   |   |
| Operating loss carryforwards before unrecognized tax position            | $ 735,958,000   |   |   |
| Operating loss carryforwards, expiration beginning dates                 | Dec. 31,  2023  |   |   |
| Unrecognized tax benefits                                                | $ 85,672,000    |   |   |
| Pennsylvania [Member]                                                    |            |   |   |
| **Income Taxes [Line Items]**                                            |            |   |   |
| Net income tax benefits                                                  | $ 26,990,000    | 24,243,000 |   |
| Deferred income tax liabilities                                          |            | 175,108,000 |   |
| Minimum [Member]                                                         |            |   |   |
| **Income Taxes [Line Items]**                                            |            |   |   |
| State corporate net income tax rates                                     | 3.00%           |   |   |
| Maximum [Member]                                                         |            |   |   |
| **Income Taxes [Line Items]**                                            |            |   |   |
| State corporate net income tax rates                                     | 9.99%           |   |   |
| Scenario, Plan [Member]                                                  |            |   |   |
| **Income Taxes [Line Items]**                                            |            |   |   |
| Statutory federal tax rate                                               | 21.00%          |   |   |
| Change in Accounting Method Accounted for as Change in Estimate [Member] |            |   |   |
| **Income Taxes [Line Items]**                                            |            |   |   |
| Regulatory assets                                                        | $ (357,262,000) | (357,262,000) |   |
| Regulatory liabilities                                                   | 303,320,000     | 303,320,000 |   |
| Impact on cash flows                                                     | $ 0             | $ 0 |   |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible domestic operating loss carryforwards. Excludes state and local operating loss carryforwards.
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| - Definition
Amount, after deferred tax asset, of deferred tax liability attributable to taxable differences without jurisdictional netting.
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| - Definition
Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.
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| - Definition
Percentage of domestic federal statutory tax rate applicable to pretax income (loss).
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| - Definition
Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to state and local income tax settlement.
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| - Definition
The increase (decrease) during the reporting period in the value of assets that are created when regulatory agencies permits public utilities to defer costs (revenues) to the balance sheet. This element is a the increase (decrease) of regulatory assets and liabilities combined.
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| - Definition
Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.
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Expiration date of each operating loss carryforward included in operating loss carryforward, in CCYY-MM-DD format.
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| - Definition
The portion of the valuation allowance pertaining to the deferred tax asset representing potential future taxable deductions from net operating loss carryforwards for which it is more likely than not that a tax benefit will not be realized.
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| - Definition
Amount of other income tax expense (benefit).
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| - Definition
Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer.
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The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period.
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| - Definition
Amount of unrecognized tax benefits.
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Additional Other Tax Expense Benefit Recorded
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Amortization Of Income Tax Catch-Up Bonus
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Deferred Income Tax Benefit, Catch-Up Bonus
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Deferred Income Tax Benefit Catch Up Bonus Impact On Net Income Loss
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Expected Tax Refund
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Tax deduction for aualifying capital expenditures made prior to 2012
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Income Taxes [Line Items]
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Operating loss carryforwards prior to being reduced by the unrecognized tax position
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