Employee Benefit Plans (Employee Savings Plans) (Details) - Employee Savings Plan [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	$ 48	$ 39	$ 118	$ 104
Duke Energy Carolinas [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	15	13	38	35
Progress Energy [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	13	12	32	30
Duke Energy Progress [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	9	8	22	21
Duke Energy Florida [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	4	4	10	9
Duke Energy Ohio [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	1	1	2	2
Duke Energy Indiana [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	2	2	5	5
Piedmont Natural Gas [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	$ 2	$ 1	$ 6	$ 3