Common Stock (Equity Securities Offering) (Details) - USD ($) shares in Millions, $ in Millions		1 Months Ended
	Feb. 20, 2018	Oct. 31, 2016	Mar. 31, 2016
Piedmont Natural Gas [Member]
Forward Contract Indexed to Issuer's Equity [Line Items]
Shares offered			10.6
Settlement Alternatives, Shares			10.6
Common stock issuances, including dividend reinvestment and employee benefits (in shares)		10.6
Proceeds from Issuance or Sale of Equity		$ 723
Subsequent Event [Member]
Forward Contract Indexed to Issuer's Equity [Line Items]
Maximum value of shares to be issued under ATM program	$ 1,000