Fair Value Measurements (Quantitative Information About Level 3 Fair Value Measurements) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 usd_per_contract	Dec. 31, 2012 usd_per_contract
Quantitative Information About Level 3 Measurements [Line Items]
Fair Value, Assets	$ 1,045	$ 705
Fair Value, Liabilities	56	118
Level 3
Quantitative Information About Level 3 Measurements [Line Items]
Fair Value, Assets	33	52
Fair Value, Liabilities	1	1
Level 3 | Electricity Congestion Contracts
Quantitative Information About Level 3 Measurements [Line Items]
Fair Value, Assets	54	71
Fair Value, Liabilities	21	20
Level 3 | Electricity Congestion Contracts | Latest Auction Pricing | Congestion Prices | Minimum
Quantitative Information About Level 3 Measurements [Line Items]
Fair Value Inputs, Price Level	(35.56)	(8.93)
Level 3 | Electricity Congestion Contracts | Latest Auction Pricing | Congestion Prices | Maximum
Quantitative Information About Level 3 Measurements [Line Items]
Fair Value Inputs, Price Level	16.06	18.03
Level 3 | Electricity Congestion Contracts | Latest Auction Pricing | Congestion Prices | Weighted Average
Quantitative Information About Level 3 Measurements [Line Items]
Fair Value Inputs, Price Level	0.08	0.19
Level 3 | Electricity Power Contracts
Quantitative Information About Level 3 Measurements [Line Items]
Fair Value, Assets	4	2
Fair Value, Liabilities	5	2
Level 3 | Electricity Power Contracts | Discounted Cash Flow | Power Prices | Minimum
Quantitative Information About Level 3 Measurements [Line Items]
Fair Value Inputs, Price Level	30.51	22.54
Level 3 | Electricity Power Contracts | Discounted Cash Flow | Power Prices | Maximum
Quantitative Information About Level 3 Measurements [Line Items]
Fair Value Inputs, Price Level	60.15	48.85
Level 3 | Electricity Power Contracts | Discounted Cash Flow | Power Prices | Weighted Average
Quantitative Information About Level 3 Measurements [Line Items]
Fair Value Inputs, Price Level	36.86	39.62
Level 3 | Netting
Quantitative Information About Level 3 Measurements [Line Items]
Fair Value, Assets	(25)	(21)
Fair Value, Liabilities	$ (25)	$ (21)