Benefit Plans (Components Of Net Periodic Benefit Cost) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 6	$ 7
Interest cost	38	41
Expected return on plan assets	(47)	(47)
Amortization of unrecognized net loss	11	7
Net periodic benefit cost	8	8
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1	2
Expected return on plan assets	(1)	(1)
Amortization of unrecognized net loss		1
Amortization of unrecognized prior service benefit	(6)	(7)
Regulatory asset decrease		1
Net periodic benefit cost	$ (6)	$ (4)