Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive loss		$ (2,230)	$ (2,275)	$ (2,300)	$ (2,057)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax		44	(257)
Other Comprehensive Income (Loss), Before Reclassifications, Tax		18	137
Reclassifications of Temporary to Permanent Equity	$ 0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		8	9
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent		70	(111)
Translation Adjustments Other Than Translation Of Balance Sheet Tax Benefit Expense		7	31
Pension and other postretirement benefit adjustments, tax cost		2	(1)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax		2	(1)
Accumulated Translation Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive loss		(1,669)	(1,733)	(1,734)	(1,567)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax		44	(257)
Other Comprehensive Income (Loss), Before Reclassifications, Tax		21	114
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		65	(143)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive loss		(562)	(545)	(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		(1)	24
Reclassifications of Temporary to Permanent Equity			84
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		7	8
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent		6	32
AOCI Attributable to Parent
Accumulated Other Comprehensive Income Loss [Line Items]
Reclassifications of Temporary to Permanent Equity	$ 107		107
Accumulated Gain (Loss), Cash Flow Hedge, Including Noncontrolling Interest [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive loss		1	3	$ 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		(2)	(1)
Reclassifications of Temporary to Permanent Equity			0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		1	1
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent		$ (1)	$ 0