Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive loss		$ (2,328)	$ (2,197)	$ (2,300)	$ (2,057)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax		(151)	(172)
Other Comprehensive Income (Loss), Before Reclassifications, Tax		110	121
Reclassifications of Temporary to Permanent Equity	$ 0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		13	18
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax		6
Tax benefit (cost) related to unrealized currency translation adjustments other than translation of foreign denominated balance sheets		39	29
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent		(28)	(33)
Pension and other postretirement benefit adjustments, tax cost		2	(3)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax		1	2
Accumulated Translation Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive loss		(1,766)	(1,641)	(1,734)	(1,567)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax		(151)	(172)
Other Comprehensive Income (Loss), Before Reclassifications, Tax		119	121
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		(32)	(51)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive loss		(564)	(557)	(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		(6)	6
Reclassifications of Temporary to Permanent Equity			84
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		10	14
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent		4	20
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		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		(3)	(6)
Reclassifications of Temporary to Permanent Equity			0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		3	4
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent		$ 0	$ (2)