Benefit Plans (Components of net periodic cost (benefit)) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost
Service cost	$ 3	$ 4
Interest cost on projected benefit obligation	34	37
Expected return on plan assets	(43)	(43)
Amortization of net actuarial (gain) loss	10	6
Net periodic (benefit) cost	4	4
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost
Interest cost on projected benefit obligation		1
Amortization of prior service cost (credit)	(4)	(5)
Amortization of net actuarial (gain) loss		1
Net periodic (benefit) cost	$ (4)	$ (3)