Fair Value Measurements (Details Textuals) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Fair Value of Financial Instruments [Line Items]
Investment excludes receivables, payables and accrued income		$ (8)	$ (3)
Cash balance excluded from available for sale securities		87	61
Investments not required to be disclosed		255	266
FES
Fair Value of Financial Instruments [Line Items]
Investment excludes receivables, payables and accrued income		3	2
Cash balance excluded from available for sale securities		$ 76	$ 44
Beaver Valley Unit 2 | NG
Fair Value of Financial Instruments [Line Items]
Transfers of decommissioning liability	$ 189