Commodity And Other Derivative Contractual Assets And Liabilities (Derivative Volumes) (Details) lb in Thousands, gal in Millions, T in Millions, MMBTU in Millions		Sep. 30, 2015 T MMBTU GWh gal lb	Dec. 31, 2014 T MMBTU GWh gal lb
Natural Gas Derivative [Member]
Derivatives, Fair Value [Line Items]
Nonmonetary Notional Volume | MMBTU	[1]	1,821	1,687
Electricity (in GWh) [Member]
Derivatives, Fair Value [Line Items]
Nonmonetary Notional Volume		43,425	22,820
Congestion Revenue RIghts (in GWh) [Member]
Derivatives, Fair Value [Line Items]
Nonmonetary Notional Volume	[1]	94,195	89,484
Coal (in tons) [Member]
Derivatives, Fair Value [Line Items]
Nonmonetary Notional Volume | T		8	10
Fuel oil (in gallons) [Member]
Derivatives, Fair Value [Line Items]
Nonmonetary Notional Volume | gal		42	36
Uranium (in pounds) [Member]
Derivatives, Fair Value [Line Items]
Nonmonetary Notional Volume | lb		126	150

[1] Represents gross forward purchases associated with instruments used to hedge electricity price differences between settlement points within ERCOT.