Commitments and Contingencies (Schedule of Environmental Loss Contingencies) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Accrual for Environmental Loss Contingencies [Roll Forward]
Balance at beginning of period	$ 81	$ 98
Provisions/adjustments	7	(1)
Cash reductions	(20)	(13)
Balance at end of period	68	84
Environmental exit costs, reasonably possible additional loss	57
Duke Energy Carolinas [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Balance at beginning of period	10	10
Provisions/adjustments	3	2
Cash reductions	(2)	(2)
Balance at end of period	11	10
Environmental exit costs, reasonably possible additional loss	17
Progress Energy [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Balance at beginning of period	15	18
Provisions/adjustments	2	1
Cash reductions	(5)	(3)
Balance at end of period	12	16
Duke Energy Progress [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Balance at beginning of period	3	3
Provisions/adjustments	3
Cash reductions	(1)
Balance at end of period	5	3
Duke Energy Florida [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Balance at beginning of period	12	14
Provisions/adjustments	(1)	1
Cash reductions	(4)	(3)
Balance at end of period	7	12
Duke Energy Ohio [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Balance at beginning of period	47	59
Provisions/adjustments	3	(3)
Cash reductions	(12)	(7)
Balance at end of period	38	49
Environmental exit costs, reasonably possible additional loss	30
Duke Energy Indiana [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Balance at beginning of period	5	10
Provisions/adjustments	1	(2)
Cash reductions	(1)	(1)
Balance at end of period	5	7
Piedmont Natural Gas [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Balance at beginning of period	2	1
Provisions/adjustments		1
Cash reductions	0
Balance at end of period	2	$ 2
Environmental exit costs, reasonably possible additional loss	$ 2