Summary of Significant Accounting Policies (Right of Use Assets and Operating Lease Liabilities) (Details) - Scenario, Forecast [Member] - Accounting Standards Update 2016-02 [Member] $ in Millions	Jan. 01, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease liability	$ 1,700
Right of use assets	1,700
Duke Energy Carolinas [Member]
Lessee, Lease, Description [Line Items]
Operating lease liability	150
Right of use assets	150
Progress Energy [Member]
Lessee, Lease, Description [Line Items]
Operating lease liability	850
Right of use assets	850
Duke Energy Progress [Member]
Lessee, Lease, Description [Line Items]
Operating lease liability	400
Right of use assets	400
Duke Energy Florida [Member]
Lessee, Lease, Description [Line Items]
Operating lease liability	450
Right of use assets	450
Duke Energy Ohio [Member]
Lessee, Lease, Description [Line Items]
Operating lease liability	25
Right of use assets	25
Duke Energy Indiana [Member]
Lessee, Lease, Description [Line Items]
Operating lease liability	60
Right of use assets	60
Piedmont Natural Gas [Member]
Lessee, Lease, Description [Line Items]
Operating lease liability	30
Right of use assets	$ 30