Benefit Plans (Termination, Settlement and Curtailment Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Termination, settlement, and curtailment costs		$ 27
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation	$ 0	23	$ 0
Net loss	86	9	8
Prior service cost (credit)	0	2	0
Termination, settlement, and curtailment costs	86	34	8
Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation		11
Net loss		0
Prior service cost (credit)		(13)
Termination, settlement, and curtailment costs	$ 0	$ (2)	$ 0