Regulatory Matters (Regulatory Matters Narrative - Piedmont) (Details) - Piedmont - Tennessee Annual Review Mechanism - TPUC - USD ($) $ in Millions	Sep. 11, 2023	May 19, 2023	Oct. 10, 2022
Public Utilities, General Disclosures [Line Items]
Approved return on equity percentage (as a percent)			9.80%
Requested rate increase (decrease), amount	$ 29	$ 42
Recovery amounts	11
Approved rate increase (decrease), amount	$ 40