Fair Value Disclosures (Reconciliations Of Fair Value Measurements Using Significant Unobservable Inputs (Level 3)) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Natural Gas [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance as of January 1	$ (23)	$ (29)
Included in income	(4)
Included in regulatory liabilities	(10)	(20)
Settlements	19	26
Transfers in (out) of Level 3	1
Ending balance as of December 31	(17)	(23)
Life Insurance Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance as of January 1	19	19
Included in income	6	3
Issuances	(3)	(3)
Settlements	(5)
Ending balance as of December 31	$ 17	$ 19