Regulatory Matters (Schedule of MISO Exit fees)(Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Restructuring Reserve [Roll Forward]
Balance, beginning of period	$ 28
Provision/adjustments	144
Cash reductions	(36)
Balance, end of period	136
Total regulatory assets	12,250	$ 12,157
Duke Energy Ohio [Member]
Restructuring Reserve [Roll Forward]
Total regulatory assets	533	$ 561
Duke Energy Ohio [Member] | RTO Realignment [Member]
Restructuring Reserve [Roll Forward]
Balance, beginning of period	94
Provision/adjustments	3
Cash reductions	(5)
Balance, end of period	92
Total regulatory assets	$ 72