Dispositions (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended		1 Months Ended	6 Months Ended	12 Months Ended		1 Months Ended		1 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Jun. 30, 2013 Illinois Gas Contracts	Jun. 30, 2013 Brayton Point and Kincaid	Dec. 31, 2013 Brayton Point and Kincaid	Dec. 31, 2013 Loss from Discontinued Operations Brayton Point and Kincaid	Aug. 31, 2013 Elwood	Dec. 31, 2013 Elwood	Aug. 31, 2013 Elwood Other Income
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sales price			$ 32
Gain on sale			29
After-tax gain on sale			18
Asset disposition adjustment	44	11	3			16
Impairment charge	1,600			48	1,600
Long-lived assets impairment charges, net of tax				28
Ownership percentage								50.00%
Proceeds from sale of equity method investment							465
Gain on sale of investment									35
After tax gain on sale of investment									25
Loss from discontinued operation					(17)
Loss on discontinued operation, net of tax					$ (18)