Benefit Plans (Components of net periodic cost (benefit)) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Pension Cost [Member]
Defined Benefit Plan, Net Periodic Benefit Cost
Service cost	$ 13	$ 16	$ 17
Interest cost on projected benefit obligation	146	149	153
Expected return on plan assets	(172)	(162)	(145)
Amortization of net actuarial (gain) loss	25	24	25
Net periodic (benefit) cost	12	27	50
Postretirement Benefit Costs [Member]
Defined Benefit Plan, Net Periodic Benefit Cost
Service cost	1	1	1
Interest cost on projected benefit obligation	3	7	9
Amortization of prior service cost (credit)	(19)	(16)	(16)
Amortization of net actuarial (gain) loss		1	1
Net periodic (benefit) cost	$ (15)	$ (7)	$ (5)