Regulatory Matters (Schedule of MISO Exit fees) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Restructuring Reserve [Roll Forward]
Balance, beginning of period	$ 19
Cash reductions	(14)
Balance, end of period	205
Total regulatory assets	15,622	$ 13,879
Duke Energy Ohio [Member]
Restructuring Reserve [Roll Forward]
Balance, end of period	2
Total regulatory assets	564	494
Duke Energy Ohio [Member] | RTO Realignment [Member]
Restructuring Reserve [Roll Forward]
Balance, beginning of period	66
Provisions/Adjustments	(4)
Cash reductions	(4)
Balance, end of period	58
Total regulatory assets	$ 43	$ 50