Long Term Debt (Details) - USD ($)	1 Months Ended	2 Months Ended
	Jan. 31, 2017	Dec. 31, 2016	Oct. 31, 2016
Debt Instrument [Line Items]
Long-term debt, principal		$ 1,835,000,000	$ 1,835,000,000
Unamortized debt issuance expenses and discounts		(13,900,000)	(14,000,000)
Long-term debt, net including current maturities		1,821,100,000	1,821,000,000
Current maturities of long-term debt		35,000,000	35,000,000
Long-term debt, net excluding current maturities		$ 1,786,100,000	$ 1,786,000,000
Senior Notes 8.51%
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		8.51%
Debt Instrument, Maturity Date		Sep. 30, 2017
Subsequent Event
Debt Instrument [Line Items]
Subsequent Event, Description	In January 2017, Duke Energy amended its registration statement to add Piedmont as a registrant, and included in the amendment a prospectus for Piedmont under which debt securities may be issued in the same manner as other Duke Energy registrants.