Pension and Postretirement Plans (Summary of Amounts Recognized in Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Net gain (loss) arising during the period	$ (1)	$ (178)	$ (138)
Curtailment gain	0	31	$ 0
Pension Benefits | United States
Defined Benefit Plan Disclosure [Line Items]
Unrecognized net actuarial loss (gain)	545	684
Unrecognized prior service cost (credit)		3
Net gain (loss) arising during the period	(14)	(54)
Amortization of loss and settlements included in income	153	80
Net change in unrecognized net actuarial loss (gain) during the period	139	26
Amortization of prior service cost (credit) included in income	3	3
Net change in unrecognized prior service cost (credit) during the period	3	3
Pension Benefits | Int’l.
Defined Benefit Plan Disclosure [Line Items]
Unrecognized net actuarial loss (gain)	190	227
Unrecognized prior service cost (credit)	(4)	(5)
Net gain (loss) arising during the period	14	(129)
Curtailment gain		31
Amortization of loss and settlements included in income	23	14
Net change in unrecognized net actuarial loss (gain) during the period	37	(84)
Amortization of prior service cost (credit) included in income	(1)	(1)
Net change in unrecognized prior service cost (credit) during the period	(1)	(1)
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Unrecognized net actuarial loss (gain)	1	(5)
Unrecognized prior service cost (credit)	(7)	(9)
Net gain (loss) arising during the period	(6)	7
Curtailment gain	0	0
Amortization of loss and settlements included in income	0	0
Net change in unrecognized net actuarial loss (gain) during the period	(6)	7
Amortization of prior service cost (credit) included in income	(2)	(1)
Net change in unrecognized prior service cost (credit) during the period	$ (2)	$ (1)