Summary of Significant Accounting Policies (Inventory) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Public Utilities, Inventory [Line Items]
Materials and supplies	$ 2,312	$ 2,297
Coal	561	586
Natural gas, oil, other	294	349
Total inventory	3,167	3,232
Duke Energy Carolinas
Public Utilities, Inventory [Line Items]
Materials and supplies	785	768
Coal	186	187
Natural gas, oil, other	39	41
Total inventory	1,010	996
Progress Energy
Public Utilities, Inventory [Line Items]
Materials and supplies	999	1,038
Coal	193	186
Natural gas, oil, other	183	199
Total inventory	1,375	1,423
Duke Energy Progress
Public Utilities, Inventory [Line Items]
Materials and supplies	673	686
Coal	131	138
Natural gas, oil, other	107	110
Total inventory	911	934
Duke Energy Florida
Public Utilities, Inventory [Line Items]
Materials and supplies	325	351
Coal	63	48
Natural gas, oil, other	76	90
Total inventory	464	489
Duke Energy Ohio
Public Utilities, Inventory [Line Items]
Materials and supplies	78	79
Coal	16	15
Natural gas, oil, other	16	41
Total inventory	110	135
Duke Energy Indiana
Public Utilities, Inventory [Line Items]
Materials and supplies	307	318
Coal	165	198
Natural gas, oil, other	1	1
Total inventory	473	517
Piedmont
Public Utilities, Inventory [Line Items]
Materials and supplies	12	5
Natural gas, oil, other	56	67
Total inventory	$ 68	$ 72