Employee Benefit Plans (Assumptions Used For Pension Benefits Accounting) (Details)	2 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Oct. 31, 2016	Dec. 31, 2015	Oct. 31, 2015
Pension Plan [Member] | Qualified Plan [Member]
Benefit Obligations [Abstract]
Discount rate	4.10%	3.60%	4.10%		4.40%
Net Periodic Benefit Cost [Abstract]
Discount rate		4.10%	4.40%		4.10%
Expected long-term rate of return on plan assets					6.50%
Pension Plan [Member] | Nonqualified Plan [Member]
Benefit Obligations [Abstract]
Discount rate	4.10%	3.60%	4.10%		4.40%
Salary increase	4.40%		4.40%		4.40%
Net Periodic Benefit Cost [Abstract]
Discount rate		4.10%	4.40%		4.10%
Salary increase		4.40%	4.40%		4.40%
Pension Plan [Member] | Minimum [Member] | Qualified Plan [Member]
Benefit Obligations [Abstract]
Salary increase	4.00%	3.50%	4.00%		4.00%
Net Periodic Benefit Cost [Abstract]
Discount rate
Salary increase		4.00%	4.00%		4.00%
Expected long-term rate of return on plan assets		6.50%	6.50%
Pension Plan [Member] | Minimum [Member] | Nonqualified Plan [Member]
Benefit Obligations [Abstract]
Salary increase		3.50%
Pension Plan [Member] | Maximum [Member] | Qualified Plan [Member]
Benefit Obligations [Abstract]
Salary increase	4.50%	4.00%	4.50%		4.40%
Net Periodic Benefit Cost [Abstract]
Salary increase		4.50%	4.40%		4.40%
Expected long-term rate of return on plan assets		6.75%	6.75%
Pension Plan [Member] | Maximum [Member] | Nonqualified Plan [Member]
Benefit Obligations [Abstract]
Salary increase		4.00%
Pension Plan [Member] | Piedmont Natural Gas [Member] | Qualified Plan [Member]
Benefit Obligations [Abstract]
Discount rate	4.10%		4.10%	3.80%		4.34%
Salary increase	4.50%		4.50%	4.05%		4.07%
Net Periodic Benefit Cost [Abstract]
Discount rate	3.80%			4.34%		4.13%
Salary increase	4.05%			4.07%		3.68%
Expected long-term rate of return on plan assets	6.75%			7.25%		7.50%
Pension Plan [Member] | Piedmont Natural Gas [Member] | Nonqualified Plan [Member]
Benefit Obligations [Abstract]
Discount rate	4.10%		4.10%	3.80%		3.85%
Net Periodic Benefit Cost [Abstract]
Discount rate	3.80%			3.85%		3.69%
Other Post-Retirement Benefit Plans [Member]
Benefit Obligations [Abstract]
Discount rate	4.10%	3.60%	4.10%		4.40%
Net Periodic Benefit Cost [Abstract]
Discount rate		4.10%	4.40%		4.10%
Expected long-term rate of return on plan assets		6.50%	6.50%		6.50%
Assumed tax rate		35.00%	35.00%		35.00%
Other Post-Retirement Benefit Plans [Member] | Piedmont Natural Gas [Member]
Benefit Obligations [Abstract]
Discount rate	4.10%		4.10%	3.80%		4.38%
Net Periodic Benefit Cost [Abstract]
Discount rate	3.80%			4.38%		4.03%
Expected long-term rate of return on plan assets	6.75%			7.25%		7.50%