Employee Benefit Plans (Components of Net Periodic Pension Costs) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Qualified Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 45	$ 40
Interest cost on projected benefit obligation	75	82
Expected return on plan assets	(140)	(136)
Amortization of actuarial loss (gain)	33	36
Amortization of prior service credit	(8)	(6)
Other		2
Net periodic costs	5	18
Qualified Pension Plan [Member] | Duke Energy Carolinas [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	15	12
Interest cost on projected benefit obligation	18	20
Expected return on plan assets	(37)	(35)
Amortization of actuarial loss (gain)	7	8
Amortization of prior service credit	(2)	(2)
Net periodic costs	1	3
Qualified Pension Plan [Member] | Progress Energy [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	13	12
Interest cost on projected benefit obligation	24	25
Expected return on plan assets	(45)	(43)
Amortization of actuarial loss (gain)	11	14
Amortization of prior service credit	(1)	(1)
Other		1
Net periodic costs	2	8
Qualified Pension Plan [Member] | Duke Energy Progress [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	7	6
Interest cost on projected benefit obligation	11	12
Expected return on plan assets	(21)	(21)
Amortization of actuarial loss (gain)	5	6
Net periodic costs	2	3
Qualified Pension Plan [Member] | Duke Energy Florida [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	5	5
Interest cost on projected benefit obligation	13	13
Expected return on plan assets	(23)	(21)
Amortization of actuarial loss (gain)	6	7
Net periodic costs	1	4
Qualified Pension Plan [Member] | Duke Energy Ohio [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	1	1
Interest cost on projected benefit obligation	5	5
Expected return on plan assets	(7)	(7)
Amortization of actuarial loss (gain)	1	1
Qualified Pension Plan [Member] | Duke Energy Indiana [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	2	2
Interest cost on projected benefit obligation	6	7
Expected return on plan assets	(10)	(11)
Amortization of actuarial loss (gain)	2	3
Net periodic costs		1
Qualified Pension Plan [Member] | Piedmont Natural Gas [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	2	3
Interest cost on projected benefit obligation	3	3
Expected return on plan assets	(6)	(6)
Amortization of actuarial loss (gain)	3	3
Amortization of prior service credit	(3)	(1)
Net periodic costs	(1)	2
Other Post-Retirement Benefit Plans [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	1	1
Interest cost on projected benefit obligation	7	9
Expected return on plan assets	(2)	(3)
Amortization of actuarial loss (gain)	1	2
Amortization of prior service credit	(5)	(29)
Net periodic costs	2	(20)
Other Post-Retirement Benefit Plans [Member] | Duke Energy Carolinas [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Interest cost on projected benefit obligation	2	2
Expected return on plan assets	(2)	(2)
Amortization of actuarial loss (gain)		(1)
Amortization of prior service credit	(1)	(2)
Net periodic costs	(1)	(3)
Other Post-Retirement Benefit Plans [Member] | Progress Energy [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Interest cost on projected benefit obligation	4	4
Amortization of actuarial loss (gain)		5
Amortization of prior service credit	(2)	(21)
Net periodic costs	2	(12)
Other Post-Retirement Benefit Plans [Member] | Duke Energy Progress [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Interest cost on projected benefit obligation	1	2
Amortization of actuarial loss (gain)		3
Amortization of prior service credit		(14)
Net periodic costs	1	(9)
Other Post-Retirement Benefit Plans [Member] | Duke Energy Florida [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Interest cost on projected benefit obligation	1	2
Amortization of actuarial loss (gain)		2
Amortization of prior service credit	(1)	(8)
Net periodic costs		$ (4)
Other Post-Retirement Benefit Plans [Member] | Duke Energy Indiana [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Interest cost on projected benefit obligation	1
Amortization of actuarial loss (gain)	1
Net periodic costs	$ 2