Benefit Plans (Components of net periodic cost (benefit)) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	$ 12	$ 13	$ 16
Interest cost	135	146	149
Expected return on plan assets	(171)	(172)	(162)
Amortization of net actuarial (gain) loss	39	25	24
Net periodic (benefit) cost	15	12	27
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost		1	1
Interest cost	2	3	7
Amortization of prior service credit	(18)	(19)	(16)
Amortization of net actuarial (gain) loss	1		1
Net periodic (benefit) cost	$ (15)	$ (15)	$ (7)