Regulatory Matters (Regulatory Matters Narrative - Piedmont) (Details) - 2020 Tennessee Rate Case - 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.

No definition available.

Name:	us-gaap_PublicUtilitiesGeneralDisclosuresLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration