Commitments and Contingencies (Nuclear Operations) (Narrative) (Detail) - USD ($)	3 Months Ended
Jun. 30, 2018	Mar. 31, 2018
Nuclear Obligations
Loss Contingencies [Line Items]
Maximum liability protection per nuclear incident amount	$ 13,100,000,000	$ 13,400,000,000

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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