Goodwill And Identifiable Intangible Assets (Amortization Expense Related to Intangible Assets (including income statement line item)) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 39	$ 35	$ 104	$ 104
Retail customer relationship [Member] | Depreciation and amortization [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization expense	6	8	18	25
Favorable purchase and sales contracts [Member] | Operating revenues/ Fuel, purchased power costs and delivery fees [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization expense	6	5	19	20
Software and other computer-related assets [Member] | Depreciation and amortization [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization expense	14	9	33	24
Environmental allowances and credits [Member] | Fuel, purchased power costs and delivery fees [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization expense	5	6	11	15
Mining development costs [Member] | Depreciation and amortization [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 8	$ 7	$ 23	$ 20