Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive loss	$ (2,224)	$ (2,005)	$ (2,300)	$ (2,057)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	31	189
Other Comprehensive Income (Loss), Before Reclassifications, Tax	43	(36)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	2	6
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	76	159
Translation Adjustments Other Than Translation Of Balance Sheet Tax Benefit Expense	17	21
Pension and other postretirement benefit adjustments, tax cost	1	(1)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax		(1)
Accumulated Translation Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive loss	(1,652)	(1,446)	(1,734)	(1,567)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	31	189
Other Comprehensive Income (Loss), Before Reclassifications, Tax	51	(45)
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	82	144
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive loss	(574)	(560)	(568)	(493)
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	(8)	14
Reclassifications of Temporary to Permanent Equity		84
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	2	3
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(6)	17
AOCI Attributable to Parent
Accumulated Other Comprehensive Income Loss [Line Items]
Reclassifications of Temporary to Permanent Equity		107
Accumulated Gain (Loss), Cash Flow Hedge, Including Noncontrolling Interest [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive loss	2	1	$ 2	$ 3
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	0	(5)
Reclassifications of Temporary to Permanent Equity		0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	3
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	$ 0	$ (2)