Benefit Plans (Components of net periodic cost (benefit)) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost
Service cost	$ 3	$ 3	$ 9	$ 10
Interest cost on projected benefit obligation	34	37	101	110
Expected return on plan assets	(43)	(44)	(128)	(130)
Amortization of net actuarial (gain) loss	10	7	29	19
Net periodic postretirement (benefit) cost	4	3	11	9
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost
Interest cost on projected benefit obligation	1	1	2	3
Amortization of prior service credit	(4)	(5)	(13)	(14)
Net periodic postretirement (benefit) cost	$ (3)	$ (4)	$ (11)	$ (11)