Benefit Plans (Components of net periodic cost (benefit)) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain	$ (86)
Settlement loss	84
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	9	12	12
Interest cost on projected benefit obligation	132	121	135
Expected return on plan assets	(191)	(181)	(171)
Amortization of net actuarial (gain) loss	25	47	39
Settlement loss	84	3
Net periodic (benefit) cost	59	2	15
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	1	0
Interest cost on projected benefit obligation	1	1	2
Amortization of prior service credit	(10)	(18)	(18)
Amortization of net actuarial (gain) loss	1	2	1
Curtailment gain	(86)
Net periodic (benefit) cost	$ (94)	$ (14)	$ (15)