Intangible Assets and Goodwill (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Jan. 02, 2018
Intangible assets
Weighted Amortizable Life (in years)			14 years		14 years
Finite-Lived Intangible Assets, Gross	$ 4,208		$ 4,208		$ 4,177
Finite-Lived Intangible Assets, Accumulated Amortization	2,169		2,169		2,066
Net	2,039		2,039		2,111
Intangible assets	2,039		2,039		$ 2,111
Amortization expense	83	$ 80	166	$ 159
Remaining six months of 2018	164		164
2019	322		322
2020	311		311
2021	293		293
2022	274		274
Thereafter	675		$ 675
Customer Relationships
Intangible assets
Weighted Amortizable Life (in years)			15 years		15 years
Finite-Lived Intangible Assets, Gross	2,467		$ 2,467		$ 2,441
Finite-Lived Intangible Assets, Accumulated Amortization	1,173		1,173		1,122
Net	1,294		$ 1,294		$ 1,319
Intellectual Property
Intangible assets
Weighted Amortizable Life (in years)			11 years		11 years
Finite-Lived Intangible Assets, Gross	1,546		$ 1,546		$ 1,538
Finite-Lived Intangible Assets, Accumulated Amortization	899		899		851
Net	647		$ 647		$ 687
Other
Intangible assets
Weighted Amortizable Life (in years)			13 years		13 years
Finite-Lived Intangible Assets, Gross	195		$ 195		$ 198
Finite-Lived Intangible Assets, Accumulated Amortization	97		97		93
Net	$ 98		$ 98		$ 105
ECM S.p.A.
Intangible assets
Finite-lived intangible assets						$ 112
Downer Freight Rail
Intangible assets
Finite-lived intangible assets						$ 5