Common Stock (Equity Securities Offering) (Details) shares in Millions	Mar. 31, 2016 shares
Piedmont Natural Gas [Member]
Forward Contract Indexed to Issuer's Equity [Line Items]
Shares offered	10.6

The number of issuer's shares to which the forward contract is indexed.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 40
-Section 50
-Paragraph 5
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=6445032&loc=d3e90205-114008

Name:	us-gaap_ForwardContractIndexedToIssuersEquityIndexedShares
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant