Derivative Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Fair value of derivatives
Derivative Assets	$ 218	$ 237
Derivative Liabilities	(238)	(281)
Current Assets
Fair value of derivatives
Derivative Assets	140	157
Deferred Charges and Other Assets
Fair value of derivatives
Derivative Assets	78	80
Current Liabilities
Fair value of derivatives
Derivative Liabilities	(78)	(106)
Noncurrent Liabilities
Fair value of derivatives
Derivative Liabilities	(160)	(175)
Commodity contracts | Current Assets
Fair value of derivatives
Derivative Assets	133	150
Commodity contracts | Deferred Charges and Other Assets
Fair value of derivatives
Derivative Assets	77	78
Commodity contracts | Current Liabilities
Fair value of derivatives
Derivative Liabilities	(72)	(94)
Commodity contracts | Noncurrent Liabilities
Fair value of derivatives
Derivative Liabilities	(52)	(37)
FTRs | Current Assets
Fair value of derivatives
Derivative Assets	7	7
FTRs | Deferred Charges and Other Assets
Fair value of derivatives
Derivative Assets	0	1
FTRs | Current Liabilities
Fair value of derivatives
Derivative Liabilities	(6)	(12)
FTRs | Noncurrent Liabilities
Fair value of derivatives
Derivative Liabilities	0	(1)
NUGs | Deferred Charges and Other Assets
Fair value of derivatives
Derivative Assets	1	1
NUGs | Noncurrent Liabilities
Fair value of derivatives
Derivative Liabilities	(108)	(137)
FES
Fair value of derivatives
Derivative Assets	214	233
Derivative Liabilities	(129)	(142)
FES | Current Assets
Fair value of derivatives
Derivative Assets	137	154
FES | Deferred Charges and Other Assets
Fair value of derivatives
Derivative Assets	77	79
FES | Current Liabilities
Fair value of derivatives
Derivative Liabilities	(77)	(104)
FES | Noncurrent Liabilities
Fair value of derivatives
Derivative Liabilities	(52)	(38)
FES | Commodity contracts | Current Assets
Fair value of derivatives
Derivative Assets	133	150
FES | Commodity contracts | Deferred Charges and Other Assets
Fair value of derivatives
Derivative Assets	77	78
FES | Commodity contracts | Current Liabilities
Fair value of derivatives
Derivative Liabilities	(72)	(94)
FES | Commodity contracts | Noncurrent Liabilities
Fair value of derivatives
Derivative Liabilities	(52)	(37)
FES | FTRs | Current Assets
Fair value of derivatives
Derivative Assets	4	4
FES | FTRs | Deferred Charges and Other Assets
Fair value of derivatives
Derivative Assets	0	1
FES | FTRs | Current Liabilities
Fair value of derivatives
Derivative Liabilities	(5)	(10)
FES | FTRs | Noncurrent Liabilities
Fair value of derivatives
Derivative Liabilities	$ 0	$ (1)