Summary of Significant Accounting Policies (Inventory)(Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Public Utilities, Inventory [Line Items]
Materials and supplies	$ 2,293	$ 2,374
Coal	603	774
Natural gas, oil, other	354	374
Total inventory	3,250	3,522
Duke Energy Carolinas [Member]
Public Utilities, Inventory [Line Items]
Materials and supplies	744	767
Coal	192	251
Natural gas, oil, other	35	37
Total inventory	971	1,055
Progress Energy [Member]
Public Utilities, Inventory [Line Items]
Materials and supplies	1,118	1,167
Coal	255	314
Natural gas, oil, other	219	236
Total inventory	1,592	1,717
Duke Energy Progress [Member]
Public Utilities, Inventory [Line Items]
Materials and supplies	774	813
Coal	139	148
Natural gas, oil, other	104	115
Total inventory	1,017	1,076
Duke Energy Florida [Member]
Public Utilities, Inventory [Line Items]
Materials and supplies	343	354
Coal	116	166
Natural gas, oil, other	115	121
Total inventory	574	641
Duke Energy Ohio [Member]
Public Utilities, Inventory [Line Items]
Materials and supplies	82	84
Coal	17	19
Natural gas, oil, other	34	34
Total inventory	133	137
Duke Energy Indiana [Member]
Public Utilities, Inventory [Line Items]
Materials and supplies	309	312
Coal	139	190
Natural gas, oil, other	2	2
Total inventory	450	504
Piedmont Natural Gas [Member]
Public Utilities, Inventory [Line Items]
Materials and supplies	2	1
Natural gas, oil, other	64	65
Total inventory	$ 66	$ 66