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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
	Dec. 31, 2017 USD ($)
Future Payment Commitments Under Purchase Obligations [Abstract]
Reduction In Future Payment Commitments	$ 309

X

- 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

X

- 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