Price Risk Management Future Year Net Unrealized Gain/Loss Recorded at Balance Sheet Date Expected to Become Realized (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014
Natural Gas [Member]
Commodity contracts:
Other Commitment, Due in Next Twelve Months	$ 7
Other Commitment, Due in Second Year	3
Other Commitment, Due in Third Year	10
Other Commitment, Due in Fourth Year	6
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Electricity	26
Unrealized Gain Loss On Derivatives [Member]
Commodity contracts:
Other Commitment, Due in Next Twelve Months	35
Other Commitment, Due in Second Year	26
Other Commitment, Due in Third Year	23
Other Commitment, Due in Fourth Year	11
Other Commitment, Due in Fifth Year	5
Other Commitment, Due after Fifth Year	57
Electricity	157
Electricity [Member]
Commodity contracts:
Other Commitment, Due in Next Twelve Months	28
Other Commitment, Due in Second Year	23
Other Commitment, Due in Third Year	13
Other Commitment, Due in Fourth Year	5
Other Commitment, Due in Fifth Year	5
Other Commitment, Due after Fifth Year	57
Electricity	$ 131