Regulatory Matters (Schedule of MISO Exit fees)(Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Restructuring Reserve [Roll Forward]
Balance, beginning of period	$ 136
Provision/adjustments	110
Cash reductions	(167)
Balance, end of period	79
Total regulatory assets	13,901	$ 12,250
Duke Energy Ohio [Member]
Restructuring Reserve [Roll Forward]
Total regulatory assets	557	533
Duke Energy Ohio [Member] | RTO Realignment [Member]
Restructuring Reserve [Roll Forward]
Balance, beginning of period	92
Provision/adjustments	3
Cash reductions	(5)
Balance, end of period	90
Total regulatory assets	$ 71	$ 72