Severance (Rollforward) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Restructuring Reserve [Roll Forward]
Balance, beginning of period	$ 79
Provision/adjustments	17
Cash reductions	(77)
Balance, end of period	19
Duke Energy Carolinas [Member]
Restructuring Reserve [Roll Forward]
Balance, beginning of period	13
Provision/adjustments	2
Cash reductions	(10)
Balance, end of period	5
Progress Energy [Member]
Restructuring Reserve [Roll Forward]
Balance, beginning of period	14
Cash reductions	(12)
Balance, end of period	2
Duke Energy Progress [Member]
Restructuring Reserve [Roll Forward]
Balance, beginning of period	6
Cash reductions	(5)
Balance, end of period	1
Duke Energy Florida [Member]
Restructuring Reserve [Roll Forward]
Balance, beginning of period	8
Cash reductions	(8)
Piedmont Natural Gas [Member]
Restructuring Reserve [Roll Forward]
Balance, beginning of period	20
Provision/adjustments	9
Cash reductions	(24)
Balance, end of period	$ 5