Benefit Plans (Components of net periodic cost (benefit)) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	$ 3	$ 3
Interest cost on projected benefit obligation	30	34
Expected return on plan assets	(45)	(43)
Amortization of net actuarial (gain) loss	12	10
Net periodic cost (benefit)		4
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Amortization of prior service credit	(4)	(4)
Net periodic cost (benefit)	$ (4)	$ (4)