Consolidated Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated provision for uncollectible accounts - customers
Consolidated Valuation and Qualifying Accounts
Beginning Balance	$ 59,266	$ 51,630	$ 40,354
Charged to Income	114,249	90,144	68,733
Charged to Other Accounts	54,199	36,373	39,775
Deductions	158,939	118,881	97,232
Ending Balance	68,775	59,266	51,630
Accumulated provision for uncollectible accounts - customers | FES
Consolidated Valuation and Qualifying Accounts
Beginning Balance	17,862	11,073	16,188
Charged to Income	7,411	21,942	14,294
Charged to Other Accounts	0	0	0
Deductions	16,807	15,153	19,409
Ending Balance	8,466	17,862	11,073
Accumulated provision for uncollectible accounts - other
Consolidated Valuation and Qualifying Accounts
Beginning Balance	5,197	2,976	4,013
Charged to Income	899	3,469	(1,464)
Charged to Other Accounts	4,189	8,264	5,208
Deductions	5,054	9,512	4,781
Ending Balance	5,231	5,197	2,976
Accumulated provision for uncollectible accounts - other | FES
Consolidated Valuation and Qualifying Accounts
Beginning Balance	2,500	2,523	2,500
Charged to Income	0	9	28
Charged to Other Accounts	0	0	0
Deductions	0	32	5
Ending Balance	2,500	2,500	2,523
Loss carryforward tax valuation reserve
Consolidated Valuation and Qualifying Accounts
Beginning Balance	174,004	125,360	101,697
Charged to Income	18,393	48,644	23,663
Charged to Other Accounts	0	0	0
Deductions	0	0	0
Ending Balance	192,397	174,004	125,360
Loss carryforward tax valuation reserve | FES
Consolidated Valuation and Qualifying Accounts
Beginning Balance	32,126	26,875	15,810
Charged to Income	13,682	5,251	11,065
Charged to Other Accounts	0	0	0
Deductions	0	0	0
Ending Balance	$ 45,808	$ 32,126	$ 26,875