Environmental Matters (Accrued Liabilities And Regulatory Assets) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Site Contingency [Line Items]
Regulatory assets	$ 9,501	$ 7,886
Manufactured Gas Plant Sites [Member]
Site Contingency [Line Items]
Accrued liabilities	422	446
Other Superfund Sites [Member]
Site Contingency [Line Items]
Accrued liabilities	67	66
Superfund Sites [Member]
Site Contingency [Line Items]
Accrued liabilities	489	512
Regulatory assets	$ 681	$ 695