Leases (Details Textuals) $ in Millions					1 Months Ended	12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	May 30, 2016	May 23, 2016 USD ($)	Nov. 30, 2014 USD ($) MW	Dec. 31, 2007	Dec. 30, 1987	Dec. 31, 2016
Leases (Textuals) [Abstract]
Period of lease terms on the portions sold by OE of its ownership interests in Perry Unit 1 and Beaver Valley Unit 2 in years							29 years
Period of lease terms on the portions sold by CEI and TE of their ownership interests in Beaver Valley Unit 2 and Bruce Mansfield Units							30 years
Beaver Valley Unit 2
Leases (Textuals) [Abstract]
Percentage leased								2.60%
Bruce Mansfield Unit 1
Leases (Textuals) [Abstract]
Percentage leased								93.83%
Perry Power Plant Unit 1
Leases (Textuals) [Abstract]
Percentage of leasehold interest related to sale leaseback arrangements				3.75%
FG
Leases (Textuals) [Abstract]
Percentage of undivided interest of FGCO in Bruce Mansfield Unit 1						93.825%
FG | Bruce Mansfield Unit 1
Leases (Textuals) [Abstract]
Basic terms of operating lease						33 years
NG | Perry Power Plant Unit 1
Leases (Textuals) [Abstract]
Payments to acquire interest in subsidiaries				$ 50
Plant ownership percentage		100.00%	100.00%
NG | Perry Power Plant Unit 1
Leases (Textuals) [Abstract]
Purchase of lessor equity interests in sale and leaseback (in MW) | MW					55.3
Purchase of lessor equity interests in sale and leaseback, value					$ 87
Forecast | NG | Perry Power Plant Unit 1
Leases (Textuals) [Abstract]
Plant ownership percentage	100.00%