Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive loss	$ (2,275)	$ (2,059)	$ (2,057)	$ (2,356)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	(257)	530
Other Comprehensive Income (Loss), Before Reclassifications, Tax	137	(254)
Reclassifications of Temporary to Permanent Equity	(107)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	9	21
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(218)	297
Translation Adjustments Other Than Translation Of Balance Sheet Tax Benefit Expense	31	(113)
Pension and other postretirement benefit adjustments, tax cost	(3)	(14)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax	(1)	(8)
Accumulated Translation Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive loss	(1,733)	(1,450)	(1,567)	(1,798)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	(257)	530
Other Comprehensive Income (Loss), Before Reclassifications, Tax	114	(182)
Reclassifications of Temporary to Permanent Equity	23
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(166)	348
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive loss	(545)	(605)	(493)	(571)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	0	0
Other Comprehensive Income (Loss), Before Reclassifications, Tax	24	(59)
Reclassifications of Temporary to Permanent Equity	84
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	8	25
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(52)	(34)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive loss	3	(4)	$ 3	$ 13
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	0	0
Other Comprehensive Income (Loss), Before Reclassifications, Tax	(1)	(13)
Reclassifications of Temporary to Permanent Equity	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	1	(4)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	$ 0	$ (17)