Supplemental Financial Statement Information (Components Of Postretirement Benefit Expense) (Details) (Postretirement Benefit Expense [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Postretirement Benefit Expense [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 1
Interest cost	5	5
Actuarial loss	2	2
Amortization of prior service credit	(7)	(6)
Net postretirement benefit expense	$ 1	$ 2