Employee Benefit Plans (Employee Savings Plans) (Details) - Employee Savings Plan [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	$ 49	$ 43	$ 167	$ 147
Duke Energy Carolinas [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	15	14	53	49
Progress Energy [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	13	12	45	42
Duke Energy Progress [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	9	9	31	30
Duke Energy Florida [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	4	4	14	13
Duke Energy Ohio [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer contributions		1	2	3
Duke Energy Indiana [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	3	2	8	7
Piedmont Natural Gas [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	$ 4	$ 2	$ 10	$ 5