Benefit Plans (Components of net periodic cost (benefit)) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost
Service cost	$ 3	$ 3	$ 6	$ 7
Interest cost on projected benefit obligation	33	36	67	73
Expected return on plan assets	(42)	(43)	(85)	(86)
Amortization of net actuarial (gain) loss	9	6	19	12
Net periodic (benefit) cost	3	2	7	6
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost
Interest cost on projected benefit obligation	1	1	1	2
Amortization of prior service cost (credit)	(5)	(4)	(9)	(9)
Amortization of net actuarial (gain) loss		(1)
Net periodic (benefit) cost	$ (4)	$ (4)	$ (8)	$ (7)