Operating leases - Future Minimum Lease Payments (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Disclosure of finance lease and operating lease by lessee [line items]
Future minimum lease payments	$ 13,970	$ 14,255
1 year
Disclosure of finance lease and operating lease by lessee [line items]
Future minimum lease payments	2,969	3,315
2 to 5 years
Disclosure of finance lease and operating lease by lessee [line items]
Future minimum lease payments	6,387	6,651
Thereafter
Disclosure of finance lease and operating lease by lessee [line items]
Future minimum lease payments	$ 4,614	$ 4,289

The amount of future minimum lease payments payable under non-cancellable operating leases. Minimum lease payments are payments over the lease term that the lessee is or can be required to make, excluding contingent rent, costs for services and taxes to be paid by, and reimbursed to, the lessor, together with: (a) for a lessee, any amounts guaranteed by the lessee or by a party related to the lessee; or (b) for a lessor, any residual value guaranteed to the lessor by: (i) the lessee; (ii) a party related to the lessee; or (iii) a third party unrelated to the lessor that is financially capable of discharging the obligations under the guarantee.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2019-01-01
-Name IAS
-Number 17
-IssueDate 2017-01-01
-Paragraph 35
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=17&date=2017-03-02&anchor=para_35_a&doctype=Standard&book=B
-URIDate 2017-03-09

Name:	ifrs-full_MinimumLeasePaymentsPayableUnderNoncancellableOperatingLease
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant