Summary of Significant Accounting Policies (Inventory) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Public Utilities, Inventory [Line Items]
Materials and supplies	$ 2,297	$ 2,238
Coal	586	491
Natural gas, oil, other	349	355
Total inventory	3,232	3,084
Duke Energy Carolinas
Public Utilities, Inventory [Line Items]
Materials and supplies	768	731
Coal	187	175
Natural gas, oil, other	41	42
Total inventory	996	948
Progress Energy
Public Utilities, Inventory [Line Items]
Materials and supplies	1,038	1,049
Coal	186	192
Natural gas, oil, other	199	218
Total inventory	1,423	1,459
Duke Energy Progress
Public Utilities, Inventory [Line Items]
Materials and supplies	686	734
Coal	138	106
Natural gas, oil, other	110	114
Total inventory	934	954
Duke Energy Florida
Public Utilities, Inventory [Line Items]
Materials and supplies	351	315
Coal	48	86
Natural gas, oil, other	90	103
Total inventory	489	504
Duke Energy Ohio
Public Utilities, Inventory [Line Items]
Materials and supplies	79	84
Coal	15	14
Natural gas, oil, other	41	28
Total inventory	135	126
Duke Energy Indiana
Public Utilities, Inventory [Line Items]
Materials and supplies	318	312
Coal	198	109
Natural gas, oil, other	1	1
Total inventory	517	422
Piedmont
Public Utilities, Inventory [Line Items]
Materials and supplies	5	2
Natural gas, oil, other	67	68
Total inventory	$ 72	$ 70