Benefit Plans (Components of net periodic cost (benefit)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 0	$ 4
Interest cost on projected benefit obligation	103	113	112
Expected return on plan assets	(154)	(160)	(174)
Amortization of net actuarial loss	35	37	34
Settlement loss	9	0	0
Net periodic pension cost (benefit)	(7)	(10)	(24)
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost on projected benefit obligation	0	0	1
Amortization of prior service credit	(2)	(2)	(3)
Amortization of net actuarial loss	0	0	1
Net periodic pension cost (benefit)	$ (2)	$ (2)	$ (1)