Pension and Other Post-Employment Benefits (Recognized Amounts In Other Comprehensive Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Amortization of net actuarial gains and losses		$ 1	$ (2)
Curtailment	$ 1
Total amounts recognized in other comprehensive (income) loss, after tax	(3)	(3)	(33)
Pension Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	1	8	(22)
Amortization of net actuarial gains and losses	(1)		(2)
Total amounts recognized in other comprehensive (income) loss, before tax		8	(24)
Total amounts recognized in other comprehensive (income) loss, after tax		6	(17)
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	(8)	(14)	(24)
Amortization of net actuarial gains and losses	1	1
Amortization of net prior service costs	1
Curtailment	1
Total amounts recognized in other comprehensive (income) loss, before tax	(5)	(13)	(24)
Total amounts recognized in other comprehensive (income) loss, after tax	$ (3)	$ (9)	$ (16)