Intangible assets and goodwill (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Oct. 01, 2016	Oct. 31, 2015
Intangible assets
Goodwill impairment charge	$ 595	$ 595	$ 0	$ 0
Goodwill	6,020	6,020	$ 6,615	6,694
Tax benefit from goodwill impairment loss		$ 17
Weighted Amortizable Life (in years)		14 years	14 years
Gross Carrying Amount	4,066	$ 4,066	$ 4,323
Accumulated Amortization	(1,717)	(1,717)	(1,502)
Net	2,349	2,349	2,821
Total intangible assets, net	2,349	2,349	2,821
Amortization expense		326	337	365
2017	313	313
2018	308	308
2019	303	303
2020	292	292
2021	275	275
Thereafter	858	$ 858
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	2,378	$ 2,378	$ 2,489
Accumulated Amortization	(934)	(934)	(809)
Net	1,444	$ 1,444	$ 1,680
Intellectual property
Intangible assets
Weighted Amortizable Life (in years)		11 years	11 years
Gross Carrying Amount	1,496	$ 1,496	$ 1,660
Accumulated Amortization	(706)	(706)	(626)
Net	790	$ 790	$ 1,034
Other
Intangible assets
Weighted Amortizable Life (in years)		14 years	12 years
Gross Carrying Amount	192	$ 192	$ 174
Accumulated Amortization	(77)	(77)	(67)
Net	115	115	107
Resource Industries
Intangible assets
Goodwill impairment charge		595	0
Goodwill	$ 2,935	2,935	$ 3,565	$ 3,707
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