Environmental Matters (Accrued Liabilities And Regulatory Assets) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Site Contingency [Line Items]
Regulatory assets	$ 9,468	$ 9,501
Manufactured Gas Plant Sites [Member]
Site Contingency [Line Items]
Accrued liabilities	466	422
Other Superfund Sites [Member]
Site Contingency [Line Items]
Accrued liabilities	71	67
Superfund Sites [Member]
Site Contingency [Line Items]
Accrued liabilities	537	489
Regulatory assets	$ 729	$ 681