Summary of Significant Accounting Policies (Inventory) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Public Utilities, Inventory [Line Items]
Materials and supplies	$ 2,238	$ 2,293
Coal	491	603
Natural gas, oil, other	355	354
Total inventory	3,084	3,250
Duke Energy Carolinas [Member]
Public Utilities, Inventory [Line Items]
Materials and supplies	731	744
Coal	175	192
Natural gas, oil, other	42	35
Total inventory	948	971
Progress Energy [Member]
Public Utilities, Inventory [Line Items]
Materials and supplies	1,049	1,118
Coal	192	255
Natural gas, oil, other	218	219
Total inventory	1,459	1,592
Duke Energy Progress [Member]
Public Utilities, Inventory [Line Items]
Materials and supplies	734	774
Coal	106	139
Natural gas, oil, other	114	104
Total inventory	954	1,017
Duke Energy Florida [Member]
Public Utilities, Inventory [Line Items]
Materials and supplies	315	343
Coal	86	116
Natural gas, oil, other	103	115
Total inventory	504	574
Duke Energy Ohio [Member]
Public Utilities, Inventory [Line Items]
Materials and supplies	84	82
Coal	14	17
Natural gas, oil, other	28	34
Total inventory	126	133
Duke Energy Indiana [Member]
Public Utilities, Inventory [Line Items]
Materials and supplies	312	309
Coal	109	139
Natural gas, oil, other	1	2
Total inventory	422	450
Piedmont Natural Gas [Member]
Public Utilities, Inventory [Line Items]
Materials and supplies	2	2
Natural gas, oil, other	68	64
Total inventory	$ 70	$ 66