Benefit Plans (Net Funded Status) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, Benefits Paid	$ (22)	$ (19)
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant	1	1
CHANGE IN PROJECTED BENEFIT OBLIGATION:
Benefit obligation, beginning period	411	374
Service cost	10	9	$ 10
Interest cost	23	21	23
Defined Benefit Plan, Benefit Obligation, Interest cost	22
Plan amendments	(1)	(4)
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Curtailment	0	0
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement	2	0
Actuarial loss	(29)	(58)
Effect of foreign currency exchange rate changes	22	(29)
Benefit obligation, ending period	470	411	374
CHANGE IN PLAN ASSETS:
Fair value of plan assets, beginning period	402	379
Actual return on plan assets	31	59
Employer contributions	18	18
Defined Benefit Plan, Plan Assets, Payment for Settlement	(2)	0
Effect of foreign currency exchange rate changes	27	(36)
Fair value of plan assets, ending period	455	402	379
Funded status as of December 31	(15)	(9)
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant	1	1
Defined Benefit Plan, Plan Assets, Benefits Paid	(22)	(19)
UNITED STATES
CHANGE IN PROJECTED BENEFIT OBLIGATION:
Benefit obligation, beginning period	1,188	1,172
Service cost	13	13	16
Interest cost	41	42	48
Plan amendments	1	0
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Curtailment	3	2
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement	0	0
Actuarial loss	(82)	(19)
Effect of foreign currency exchange rate changes	0	0
Benefit obligation, ending period	1,257	1,188	1,172
CHANGE IN PLAN ASSETS:
Fair value of plan assets, beginning period	1,044	1,021
Actual return on plan assets	141	61
Employer contributions	13	22
Defined Benefit Plan, Plan Assets, Payment for Settlement	0	0
Effect of foreign currency exchange rate changes	0	0
Fair value of plan assets, ending period	1,127	1,044	$ 1,021
Funded status as of December 31	(130)	(144)
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant	0	0
Defined Benefit Plan, Plan Assets, Benefits Paid	$ (71)	$ (60)