Intangible Assets and Goodwill (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Jan. 02, 2018
Intangible assets
Weighted Amortizable Life (in years)	14 years		14 years
Finite-Lived Intangible Assets, Gross	$ 4,293		$ 4,177
Finite-Lived Intangible Assets, Accumulated Amortization	2,130		2,066
Net	2,163		2,111
Intangible assets	2,163		$ 2,111
Amortization expense	83	$ 79
Remaining nine months of 2018	251
2019	328
2020	317
2021	299
2022	279
Thereafter	$ 689
Customer Relationships
Intangible assets
Weighted Amortizable Life (in years)	15 years		15 years
Finite-Lived Intangible Assets, Gross	$ 2,527		$ 2,441
Finite-Lived Intangible Assets, Accumulated Amortization	1,159		1,122
Net	$ 1,368		$ 1,319
Intellectual Property
Intangible assets
Weighted Amortizable Life (in years)	11 years		11 years
Finite-Lived Intangible Assets, Gross	$ 1,569		$ 1,538
Finite-Lived Intangible Assets, Accumulated Amortization	878		851
Net	$ 691		$ 687
Other
Intangible assets
Weighted Amortizable Life (in years)	13 years		13 years
Finite-Lived Intangible Assets, Gross	$ 197		$ 198
Finite-Lived Intangible Assets, Accumulated Amortization	93		93
Net	$ 104		$ 105
ECM S.p.A.
Intangible assets
Finite-lived intangible assets				$ 112
Downer Freight Rail
Intangible assets
Finite-lived intangible assets				$ 5