Regulatory Matters (Regulatory Matters Narrative - Piedmont) (Details) - Subsequent event - 2020 Tennessee Rate Case [Member] - TPUC - Piedmont Natural Gas $ in Millions	Jul. 02, 2020 USD ($)
Public Utilities, General Disclosures [Line Items]
Requested rate increase (decrease), amount	$ 30
Increase in Annual Revenue, Percent	15.00%

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.

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