Pension and Other Post-Employment Benefits (Changes In Benefit Obligation And Fair Value Of Plan Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets, Beginning of Year	$ 194
Fair Value of Plan Assets, End of Year	210	$ 194
Non-Current Liabilities	(116)	(124)
Pension Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected Benefit Obligation, Beginning of Year	211	212
Service cost	1	2	$ 2
Interest cost	7	8	9
Actuarial (gains) losses	7	6
Exchange differences	15	6
Benefits paid (Change in Benefit Obligations)	(15)	(23)
Projected Benefit Obligation, End of Year	226	211	212
Fair Value of Plan Assets, Beginning of Year	194	208
Actual return on plan assets	15	9
Exchange differences	14	7
Employer contributions	2
Benefits Paid (Change in Plan Assets)	(15)	(23)
Transfers to defined contributions plan		(7)
Fair Value of Plan Assets, End of Year	210	194	208
Funded Status of Plan Assets, End of Year	(16)	(17)
Other Assets	4	1
Non-Current Liabilities	(20)	(18)
Total Recognized Amounts in the Consolidated Balance Sheet	(16)	(17)
Net actuarial (gain) loss	28	28
Prior service costs	(5)	(5)
Total recognized in accumulated other comprehensive income before tax	23	23
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected Benefit Obligation, Beginning of Year	92	96
Service cost	8	10	10
Interest cost	3	4	4
Actuarial (gains) losses	(8)	(14)
Exchange differences		2
Employee contributions (Change in Benefit Obligations)	1	1
Benefits paid (Change in Benefit Obligations)	(6)	(7)
Curtailment	(5)
Projected Benefit Obligation, End of Year	85	92	$ 96
Employee Contributions (Change in Plan Assets)	1	1
Employer contributions	5	6
Benefits Paid (Change in Plan Assets)	(6)	(7)
Funded Status of Plan Assets, End of Year	(85)	(92)
Current Liabilities	(7)	(7)
Non-Current Liabilities	(78)	(85)
Total Recognized Amounts in the Consolidated Balance Sheet	(85)	(92)
Net actuarial (gain) loss	(35)	(28)
Prior service costs	(5)	(7)
Total recognized in accumulated other comprehensive income before tax	$ (40)	$ (35)