Intangible assets and goodwill (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Oct. 01, 2016	Dec. 01, 2015	Oct. 31, 2015
Intangible assets
Goodwill impairment charge	$ 595	$ 0	$ 595	$ 0
Goodwill	6,200	$ 6,200	6,020	6,615
Tax benefit from goodwill impairment loss			$ 17
Weighted Amortizable Life (in years)		14 years	14 years
Gross Carrying Amount	4,177	$ 4,177	$ 4,066
Accumulated Amortization	(2,066)	(2,066)	(1,717)
Net	2,111	2,111	2,349
Total intangible assets, net	2,111	2,111	2,349
Amortization expense		323	$ 326	337
2018	322	322
2019	316	316
2020	305	305
2021	287	287
2022	268	268
Thereafter	613	$ 613
Rail Product Solutions Inc.
Intangible assets
Goodwill							$ 53
Finite-lived intangible assets							$ 82
RDS Manufacturing Inc.
Intangible assets
Goodwill						$ 59
Customer relationships
Intangible assets
Weighted Amortizable Life (in years)		15 years	15 years
Gross Carrying Amount	2,441	$ 2,441	$ 2,378
Accumulated Amortization	(1,122)	(1,122)	(934)
Net	1,319	$ 1,319	$ 1,444
Intellectual property
Intangible assets
Weighted Amortizable Life (in years)		11 years	11 years
Gross Carrying Amount	1,538	$ 1,538	$ 1,496
Accumulated Amortization	(851)	(851)	(706)
Net	687	$ 687	$ 790
Other
Intangible assets
Weighted Amortizable Life (in years)		13 years	14 years
Gross Carrying Amount	198	$ 198	$ 192
Accumulated Amortization	(93)	(93)	(77)
Net	105	105	115
Resource Industries
Intangible assets
Goodwill impairment charge		0	595
Goodwill	$ 3,057	$ 3,057	2,935	$ 3,565
Impairment of Intangible Assets, Finite-lived			132
Resource Industries | Customer relationships
Intangible assets
Impairment of Finite-lived Intangible Assets, Gross			96
Impairment of Finite-lived Intangible Assets, Accumulated Amortization			27
Resource Industries | Intellectual property
Intangible assets
Impairment of Finite-lived Intangible Assets, Gross			111
Impairment of Finite-lived Intangible Assets, Accumulated Amortization			$ 48
Surface Mining & Technology
Intangible assets
Goodwill					$ 629