Future year net unrealized gain/loss recorded at balance sheet date expected to become realized (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013
Electricity [Member]
Commodity contracts:
Other Commitment, Due in Next Twelve Months	$ 11
Other Commitment, Due in Second Year	26
Other Commitment, Due in Third Year	12
Other Commitment, Due in Fourth Year	5
Other Commitment, Due in Fifth Year	5
Other Commitment, Due after Fifth Year	58
Total	117
Natural Gas [Member]
Commodity contracts:
Other Commitment, Due in Next Twelve Months	25
Other Commitment, Due in Second Year	10
Other Commitment, Due in Third Year	14
Other Commitment, Due in Fourth Year	10
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Total	59
Unrealized Gain Loss On Derivatives [Member]
Commodity contracts:
Other Commitment, Due in Next Twelve Months	36
Other Commitment, Due in Second Year	36
Other Commitment, Due in Third Year	26
Other Commitment, Due in Fourth Year	15
Other Commitment, Due in Fifth Year	5
Other Commitment, Due after Fifth Year	58
Total	$ 176