Commitments and Contingencies Commitments and Contingencies - Commitments Table (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Contractual Obligation [Line Items]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	$ 6
Operating Leases, Future Minimum Payments, Due in Two Years	5
Operating Leases, Future Minimum Payments, Due in Three Years	4
Operating Leases, Future Minimum Payments, Due in Four Years	4
Operating Leases, Future Minimum Payments, Due in Five Years	4
Operating Leases, Future Minimum Payments, Due Thereafter	49
Operating Leases, Future Minimum Payments Due	72
Contractual Obligation, Due in Next Twelve Months	1,461
Contractual Obligation, Due in Second Year	945
Contractual Obligation, Due in Third Year	769
Contractual Obligation, Due in Fourth Year	708
Contractual Obligation, Due in Fifth Year	627
Contractual Obligation, Due after Fifth Year	3,100
Contractual Obligation	7,610
Rent expense for power purchase agreements meeting definition of a lease	24	19	28
Maximum percentage of energy sources for which a share of operating costs and debt service is required	5.00%	5.00%	5.00%
Rent expense	16	14	18
Purchased electricity contracts [Member]
Contractual Obligation [Line Items]
Purchase Obligation, Due in Next Twelve Months	119
Purchase Obligation, Due in Second Year	116
Purchase Obligation, Due in Third Year	100
Purchase Obligation, Due in Fourth Year	76
Purchase Obligation, Due in Fifth Year	72
Purchase Obligation, Due after Fifth Year	503
Purchase Obligation	986
Fuel contracts [Member]
Contractual Obligation [Line Items]
Purchase Obligation, Due in Next Twelve Months	765
Purchase Obligation, Due in Second Year	570
Purchase Obligation, Due in Third Year	514
Purchase Obligation, Due in Fourth Year	516
Purchase Obligation, Due in Fifth Year	451
Purchase Obligation, Due after Fifth Year	1,776
Purchase Obligation	4,592
Construction commitments [Member]
Contractual Obligation [Line Items]
Purchase Obligation, Due in Next Twelve Months	404
Purchase Obligation, Due in Second Year	121
Purchase Obligation, Due in Third Year	37
Purchase Obligation, Due in Fourth Year	9
Purchase Obligation, Due in Fifth Year	9
Purchase Obligation, Due after Fifth Year	37
Purchase Obligation	617
Transmission [Member]
Contractual Obligation [Line Items]
Purchase Obligation, Due in Next Twelve Months	115
Purchase Obligation, Due in Second Year	105
Purchase Obligation, Due in Third Year	98
Purchase Obligation, Due in Fourth Year	87
Purchase Obligation, Due in Fifth Year	79
Purchase Obligation, Due after Fifth Year	656
Purchase Obligation	1,140
Maintenance, service and other contracts [Member]
Contractual Obligation [Line Items]
Purchase Obligation, Due in Next Twelve Months	52
Purchase Obligation, Due in Second Year	28
Purchase Obligation, Due in Third Year	16
Purchase Obligation, Due in Fourth Year	16
Purchase Obligation, Due in Fifth Year	12
Purchase Obligation, Due after Fifth Year	79
Purchase Obligation	$ 203