Accounting Policies - Leases (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Jun. 30, 2019
Disclosure of significant accounting policies [Abstract]
Operating lease commitments reported as at 31 December 2018 under IAS 17	$ 1,717
Leases expiring in 12 months or fewer	(130)	$ (260)
Committed leases not commenced (undiscounted)	(133)
Components excluded from the lease liability (undiscounted)	(169)
Cost of reasonably certain extensions (undiscounted)	324
Other	103
Sub total	1,712
Differential on measurement of any residual value guarantees - undiscounted	(420)
Lease liability opening balance reported as at 1 January 2019 under IFRS 16	$ 1,292

The amount of current lease liabilities. [Refer: Lease liabilities]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2019-01-01
-Name IFRS
-Number 16
-IssueDate 2018-01-01
-Paragraph 47
-Subparagraph b
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=16&date=2018-03-01&anchor=para_47_b&doctype=Standard
-URIDate 2018-03-16

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- Definition

The amount of the discounted unguaranteed residual value of assets subject to finance leases. Unguaranteed residual value is the portion of the residual value of the underlying asset, the realisation of which by a lessor is not assured or is guaranteed solely by a party related to the lessor. Finance lease is a lease that transfers substantially all the risks and rewards incidental to ownership of an underlying asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2019-01-01
-Name IFRS
-Number 16
-IssueDate 2018-01-01
-Paragraph 94
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=16&date=2018-03-01&anchor=para_94&doctype=Standard
-URIDate 2018-03-16

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- Definition

The amount of the expense relating to variable lease payments not included in the measurement of lease liabilities. Variable lease payments are the portion of payments made by a lessee to a lessor for the right to use an underlying asset during the lease term that varies because of changes in facts or circumstances occurring after the commencement date, other than the passage of time. [Refer: Lease liabilities]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2019-01-01
-Name IFRS
-Number 16
-IssueDate 2018-01-01
-Paragraph 53
-Subparagraph e
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=16&date=2018-03-01&anchor=para_53_e&doctype=Standard
-URIDate 2018-03-16

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- Definition

The amount of liabilities related to the entity's leases. Lease is a contract, or part of a contract, that conveys the right to use an underlying asset for a period of time in exchange for consideration.

+ References

+ Details

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- Definition

The portion of operating lease payments 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 any amounts guaranteed by the lessee or by a party related to the lessee recognised as an expense.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2019-01-01
-Name IAS
-Number 17
-IssueDate 2018-01-01
-Paragraph 35
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=17&date=2018-03-02&anchor=para_35_c&doctype=Standard&book=b
-URIDate 2018-03-16

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- Definition

Committed Leases Not Commenced

+ References

No definition available.

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- Definition

Components Excluded From Lease Liability

+ References

No definition available.

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- Definition

Cost Of Reasonably Certain Extensions

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No definition available.

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- Definition

Disclosure of significant accounting policies [Abstract]

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- Definition

Operating Lease Commitment

+ References

No definition available.

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