Property, plant and equipment - Narrative (Detail) (Insurance and Other [Member], Equipment lease fleet [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Insurance and Other [Member] \| Equipment lease fleet [Member]
Property, Plant and Equipment [Line Items]
Future minimum lease rentals to be received, 2013	$ 730
Future minimum lease rentals to be received, 2014	574
Future minimum lease rentals to be received, 2015	436
Future minimum lease rentals to be received, 2016	314
Future minimum lease rentals to be received, 2017	193
Future minimum lease rentals to be received, thereafter	$ 245

Future rental payments receivable within one year of the balance sheet date under an operating lease.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 50

-Paragraph 4

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6454179&loc=d3e41551-112718

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 13

-Paragraph 23

-Subparagraph b(ii)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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Period Type:	instant

- Definition

Future rental payments receivable within the fifth year from the balance sheet date under an operating lease.

+ References

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- Definition

Future rental payments receivable within the fourth year from the balance sheet date under an operating lease.

+ References

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- Definition

Future rental payments receivable within the third year from the balance sheet date under an operating lease.

+ References

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- Definition

Future rental payments receivable within the second year from the balance sheet date under an operating lease.

+ References

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- Definition

Future minimum lease payments receivable under operating leases for periods greater than five years following the balance sheet date.

+ References

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