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Cash and cash equivalents - Additional information (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017
Disclosure of cash and cash equivalents [Line Items] |  |
Restricted cash and cash equivalents | $ 186 | $ 290
Repayment of third party borrowings | 142 | 158
Subsidiaries [Member] |  |
Disclosure of cash and cash equivalents [Line Items] |  |
Restricted cash and cash equivalents | 1,090 | 1,089
Repayment of third party borrowings | $ 864 | $ 703

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- Definition The amount of cash and cash equivalents whose use or withdrawal is restricted. [Refer: Cash and cash equivalents] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 55 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_55&doctype=Standard -URIDate 2017-03-09 + Details
Name: | ifrs-full_RestrictedCashAndCashEquivalents
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Disclosure of cash and cash equivalents [Line Items] + References No definition available. + Details
Name: | rio_DisclosureOfCashAndCashEquivalentsLineItems
Namespace Prefix: | rio_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Restricted cash and cash equivalent available to repay borrowings. + References No definition available. + Details
Name: | rio_RestrictedCashAndCashEquivalentAvailableToRepayBorrowings
Namespace Prefix: | rio_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Details
Name: | dei_LegalEntityAxis=ifrs-full_SubsidiariesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |