Stockholders' Equity - Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		12 Months Ended
	Jan. 01, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Changes in Accumulated Other Comprehensive Income (Loss)
Beginning balance	$ 4,589	$ 3,258	$ 4,589	$ 4,259
Adoption of new accounting guidance related to reclassification of certain tax effects	45	0	45	0
Ending balance		3,030	3,258	4,589
Accumulated Other Comprehensive Income (Loss)
Changes in Accumulated Other Comprehensive Income (Loss)
Beginning balance	$ (1,287)	(1,677)	(1,287)	(1,807)
Ending balance		(1,705)	(1,677)	(1,287)
Accumulated Foreign Currency Adjustment
Changes in Accumulated Other Comprehensive Income (Loss)
Foreign currency translation / Pension and other postretirement benefit adjustments, before reclassifications, before tax		7	(308)	294
Foreign currency translation / Pension and other postretirement benefit adjustments reclassified to income, before tax		0	5	2
Income taxes		(9)	(25)	110
Total foreign currency translation / Pension and other postretirement benefit adjustments, net of tax		(2)	(328)	406
Accumulated Defined Benefit Plans Adjustment
Changes in Accumulated Other Comprehensive Income (Loss)
Foreign currency translation / Pension and other postretirement benefit adjustments, before reclassifications, before tax		(54)	(64)	96
Foreign currency translation / Pension and other postretirement benefit adjustments reclassified to income, before tax		21	41	56
Income taxes		7	6	(38)
Total foreign currency translation / Pension and other postretirement benefit adjustments, net of tax		$ (26)	$ (17)	$ 114