Significant Accounting Policies (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended
Jun. 30, 2026	Sep. 30, 2026
Significant Accounting Policies [Line Items]
Decrease in asset retirement obligation associated with decommissioning of millstone	$ 208
Asset retirement obligation benefit associated with decommissioning of millstone unit one	195
Asset retirement obligation benefit associated with decommissioning of millstone unit one net of tax	142
Increase in asset retirement obligation with corresponding increase to regulatory assets	$ 203
Stonepeak \| OSWP
Significant Accounting Policies [Line Items]
Percentage of equity interest sold to noncontrolling interest owners		50.00%

Asset retirement obligation benefit associated with decommissioning of millstone unit one.

No definition available.

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Asset retirement obligation benefit associated with decommissioning of millstone unit one net of tax.

No definition available.

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Increase decrease in asset retirement obligation associated with decommissioning of millstone.

No definition available.

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Increase decrease in asset retirement obligation with corresponding increase to regulatory assets.

No definition available.

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[Line Items] for Significant Accounting Policies [Table]

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The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

No definition available.

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