Financial instruments and risk management - Summary of financial instruments carried at fair value (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Financial Instruments [Line Items]
Cash and cash equivalents	$ 10,773	$ 10,550
Investments in equity shares and funds	130
Equity shares and quoted funds	130	136
Other investments, including loans	2,782	1,152
Trade and other financial receivables	3,007	2,985
Financial assets (excluding derivative assets)	16,692	14,823
Forward contracts and option contracts: designated as hedges(f) (Section B)	8
Forward contracts and option contracts, not designated as hedges	334	(87)
Derivatives related to net debt	(288)	(177)
Trade and other financial payables	(5,552)	(5,922)
Total	11,194	8,637
Fair value [member] \| Level 1 [member]
Disclosure Of Financial Instruments [Line Items]
Cash and cash equivalents	7,994
Investments in equity shares and funds	92
Equity shares and quoted funds		88
Other investments, including loans	2,544	1,037
Trade and other financial receivables	20
Financial assets (excluding derivative assets)	10,650	1,125
Total	10,650	1,125
Fair value [member] \| Level 2 [member]
Disclosure Of Financial Instruments [Line Items]
Trade and other financial receivables	972	90
Financial assets (excluding derivative assets)	972	90
Forward contracts and option contracts, not designated as hedges	(25)	11
Derivatives related to net debt	(288)	(177)
Trade and other financial payables	(39)	(15)
Total	620	(91)
Fair value [member] \| Level 3 [member]
Disclosure Of Financial Instruments [Line Items]
Investments in equity shares and funds	38
Equity shares and quoted funds		3
Other investments, including loans	232	88
Financial assets (excluding derivative assets)	270	91
Forward contracts and option contracts: designated as hedges(f) (Section B)	8
Forward contracts and option contracts, not designated as hedges	359	(98)
Total	637	(7)
Not held at fair value [member]
Disclosure Of Financial Instruments [Line Items]
Cash and cash equivalents	2,779	10,550
Equity shares and quoted funds		45
Other investments, including loans	6	27
Trade and other financial receivables	2,015	2,895
Financial assets (excluding derivative assets)	4,800	13,517
Trade and other financial payables	(5,513)	(5,907)
Total	$ (713)	$ 7,610

The amount of cash on hand and demand deposits, along with short-term, highly liquid investments that are readily convertible to known amounts of cash and that are subject to an insignificant risk of changes in value. [Refer: Cash; Cash equivalents]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 7
-IssueDate 2017-01-01
-Paragraph 45
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=7&date=2017-03-01&anchor=para_45&doctype=Standard
-URIDate 2017-03-09

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 12
-IssueDate 2017-01-01
-Paragraph B13
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=12&date=2017-03-01&anchor=para_B13_a&doctype=Appendix&seq=2
-URIDate 2017-03-09

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2017-01-01
-Paragraph 54
-Subparagraph i
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_54_i&doctype=Standard
-URIDate 2017-03-09

+ Details

Name:	ifrs-full_CashAndCashEquivalents
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

+ References

No definition available.

+ Details

Name:	ifrs-full_DisclosureOfFinancialInstrumentsLineItems
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The fair value of financial instruments designated as hedging instruments. Hedging instruments are designated derivatives or (for a hedge of the risk of changes in foreign currency exchange rates only) designated non-derivative financial assets or non-derivative financial liabilities whose fair value or cash flows are expected to offset changes in the fair value or cash flows of a designated hedged item. [Refer: At fair value [member]; Derivatives [member]; Derivative financial assets; Derivative financial liabilities; Financial instruments, class [member]; Financial assets; Financial liabilities]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2018-01-01
-Name IFRS
-Number 7
-IssueDate 2017-01-01
-Paragraph 22
-Subparagraph b
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-02&anchor=para_22_b&doctype=Standard&book=B
-URIDate 2017-03-09

+ Details

Name:	ifrs-full_FinancialInstrumentsDesignatedAsHedgingInstrumentsAtFairValue
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Derivative financial liabilities related to net debt at fair value.

+ References

No definition available.

+ Details

Name:	rio_DerivativeFinancialLiabilitiesRelatedToNetDebtAtFairValue
Namespace Prefix:	rio_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The combined total of the non-current and current portions of equity shares and quoted funds classified as other financial assets.

+ References

No definition available.

+ Details

Name:	rio_EquitySharesAndQuotedFunds
Namespace Prefix:	rio_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Financial assets and liabilities net.

+ References

No definition available.

+ Details

Name:	rio_FinancialAssetsAndLiabilitiesNet
Namespace Prefix:	rio_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Financial assets net excluding derivative assets.

+ References

No definition available.

+ Details

Name:	rio_FinancialAssetsNetExcludingDerivativeAssets
Namespace Prefix:	rio_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Financial instruments not designated as hedging instruments at fair value.

+ References

No definition available.

+ Details

Name:	rio_FinancialInstrumentsNotDesignatedAsHedgingInstrumentsAtFairValue
Namespace Prefix:	rio_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Investments in equity shares and funds.

+ References

No definition available.

+ Details

Name:	rio_InvestmentsInEquitySharesAndFunds
Namespace Prefix:	rio_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Other investments, including loans.

+ References

No definition available.

+ Details

Name:	rio_OtherInvestmentsIncludingLoans
Namespace Prefix:	rio_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Trade and other financial payables.

+ References

No definition available.

+ Details

Name:	rio_TradeAndOtherFinancialPayables
Namespace Prefix:	rio_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Trade and other financial receivables.

+ References

No definition available.

+ Details

Name:	rio_TradeAndOtherFinancialReceivables
Namespace Prefix:	rio_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	ifrs-full_MeasurementAxis=ifrs-full_AtFairValueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_LevelsOfFairValueHierarchyAxis=ifrs-full_Level1OfFairValueHierarchyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_LevelsOfFairValueHierarchyAxis=ifrs-full_Level2OfFairValueHierarchyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_LevelsOfFairValueHierarchyAxis=ifrs-full_Level3OfFairValueHierarchyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_MeasurementAxis=rio_NotHeldAtFairValueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: