Pension And Other Postretirement Benefits (Amounts Recognized In Consolidated Balance Sheets) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets	$ 2,196	$ 1,915
Current liabilities	1,861	1,797
Pension benefit obligation	424	332
Other postretirement benefit obligations	469	429
Deferred income taxes, net	2,863	2,714
Accumulated other comprehensive loss, net of tax	(63)	(106)	(138)	(155)
Parent Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Current liabilities	501	248
Accumulated other comprehensive loss, net of tax	(63)	(106)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets	794	655
Current liabilities	6	6
Pension benefit obligation	424	332
Deferred income taxes, net	15	12
Accumulated other comprehensive loss, net of tax	24	17
Net amount recognized	403	346
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets	243	193
Other postretirement benefit obligations	469	429
Net amount recognized	$ (226)	$ (236)