Employee Benefit Plans (Plan Contributions) (Details) - Qualified Pension Plan [Member] - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year	$ 148,000,000
Contributions by Employer	141,000,000	$ 0
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year	7,000,000
Duke Energy Carolinas [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year	46,000,000
Contributions by Employer	46,000,000
Progress Energy [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year	45,000,000
Contributions by Employer	45,000,000
Duke Energy Progress [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year	25,000,000
Contributions by Employer	25,000,000
Duke Energy Florida [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year	20,000,000
Contributions by Employer	20,000,000
Duke Energy Indiana [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year	8,000,000
Contributions by Employer	8,000,000
Piedmont Natural Gas [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year	7,000,000
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year	$ 7,000,000