Benefit Plans (Components of net periodic cost (benefit)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 0	$ 0
Interest cost on projected benefit obligation	93	103	113
Expected return on plan assets	(159)	(154)	(160)
Amortization of net actuarial (gain) loss	37	35	37
Settlement loss	6	9	0
Total non-service cost (benefit)	(23)	(7)	(10)
Total net periodic pension cost (benefit)	(23)	(7)	(10)
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0
Interest cost on projected benefit obligation	0	0
Amortization of prior service credit	(1)	(2)	(2)
Amortization of net actuarial (gain) loss	(1)	0	0
Total non-service cost (benefit)	(2)	(2)	(2)
Total net periodic pension cost (benefit)	$ (2)	$ (2)	$ (2)