Benefit Plans (Components of net periodic cost (benefit)) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	$ 3	$ 3	$ 6	$ 6
Interest cost on projected benefit obligation	30	33	60	67
Expected return on plan assets	(45)	(42)	(90)	(85)
Amortization of net actuarial (gain) loss	12	9	24	19
Net periodic cost (benefit)		3		7
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Interest cost on projected benefit obligation	1	1	1	1
Amortization of prior service credit	(5)	(5)	(9)	(9)
Net periodic cost (benefit)	$ (4)	$ (4)	$ (8)	$ (8)