Employee Benefit Plans (Employee Savings Plans) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	$ 70	$ 65
Duke Energy Carolinas [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	23	22
Progress Energy [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	19	18
Duke Energy Progress [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	13	13
Duke Energy Florida [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	6	5
Duke Energy Ohio [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	1	1
Duke Energy Indiana [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	3	3
Piedmont Natural Gas [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	$ 4	$ 2