Subsequent Events (Details) (Subsequent Event [Member], Atlantic Coast Pipeline [Member], USD $) In Billions, unless otherwise specified	0 Months Ended
	Sep. 02, 2014	Sep. 02, 2014
Subsequent Event [Line Items]
Subsequent event, description	On September 2, 2014, Piedmont, Duke Energy Corporation (Duke Energy), Dominion Resources, Inc. (Dominion), and AGL Resources, Inc. (AGL) announced the formation of Atlantic Coast Pipeline, LLC (ACP), a Delaware limited liability company. ACP intends to construct, operate and maintain a 550 mile natural gas pipeline, with associated compression, from West Virginia through Virginia into eastern North Carolina. The pipeline will provide wholesale natural gas transportation services for Marcellus and Utica gas supplies into southeastern markets. ACP, which will be regulated by the FERC, will be designed with an initial capacity of 1.5 billion cubic feet per day with a target in-service date of late 2018. The capacity of ACP will be substantially subscribed by utilities and related companies, including us, under twenty-year contracts, subject to state regulatory approval. We entered into an agreement through a wholly owned subsidiary to become a 10% equity member of ACP. The other members are subsidiaries of Duke Energy, Dominion and AGL. A Dominion subsidiary will be the operator of the pipeline. The cost for the development and construction of the pipeline is expected to cost between $4.5 billion to $5 billion.
Membership interest percentage		10.00%
Long term purchase commitment time period	20 years
Minimum [Member]
Subsequent Event [Line Items]
Expected pipeline development and construction costs	$ 4.5	$ 4.5
Maximum [Member]
Subsequent Event [Line Items]
Expected pipeline development and construction costs	$ 5.0	$ 5.0