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Contingencies and commitments - Summary of aggregate amount of future payment commitments under purchase obligations outstanding (Parenthetical) (Detail) $ in Millions | 12 Months Ended
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Dec. 31, 2017 USD ($)
Future Payment Commitments Under Purchase Obligations [Abstract] |
Reduction In Future Payment Commitments | $ 309

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- Definition Future payment commitments under purchase obligations abstract. + References No definition available. + Details
Name: | rio_FuturePaymentCommitmentsUnderPurchaseObligationsAbstract
Namespace Prefix: | rio_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition ReductionIn future payment commitments. + References No definition available. + Details
Name: | rio_ReductionInFuturePaymentCommitments
Namespace Prefix: | rio_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration