Derivative Instruments and Hedging Activities (Commodity Derivatives) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 MWh
Derivative [Line Items]
Derivative, notional amount	$ 3,600
Power MWh | Commodity Contract
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	5,000,000
Derivative average remaining maturity	3 years	[1]

[1] Represents the remaining tenor of our commodity derivatives weighted by the corresponding volume. These derivatives range in maturity through 2016.