Regulatory Matters (Schedule of MISO Exit fees)(Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Restructuring Reserve [Roll Forward]
Balance, beginning of period	$ 79
Cash reductions	(77)
Balance, end of period	19
Total regulatory assets	13,879	$ 13,901
Duke Energy Ohio [Member]
Restructuring Reserve [Roll Forward]
Total regulatory assets	494	557
Duke Energy Ohio [Member] | RTO Realignment [Member]
Restructuring Reserve [Roll Forward]
Balance, beginning of period	90
Provisions/Adjustments	(20)
Cash reductions	(4)
Balance, end of period	66
Total regulatory assets	$ 50	$ 71