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Goodwill - Key assumptions calculation of fair value less costs of disposal (Parenthetical) (Detail) - Richards Bay Minerals [member] | 12 Months Ended |
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Dec. 31, 2017 | Dec. 31, 2016
Disclosure of key assumptions calculation of fair value less costs of disposal [Line Items] |  |
Increase in the discount rate applied to post-tax cash flows | 8.70% | 9.00%
5% decrease in the titanium slag price [member] | Titanium [member] |  |
Disclosure of key assumptions calculation of fair value less costs of disposal [Line Items] |  |
Percentage of decrease in the titanium slag price | 5.00% |
1% increase in the discount rate applied to post-tax cash flows [member] |  |
Disclosure of key assumptions calculation of fair value less costs of disposal [Line Items] |  |
Increase in the discount rate applied to post-tax cash flows | 1.00% |
10% strengthening of South African rand [member] |  |
Disclosure of key assumptions calculation of fair value less costs of disposal [Line Items] |  |
Strengthening percentage of the South African rand | 10.00% |

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- Definition The discount rate used in the current measurement of fair value less costs of disposal. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 36 -IssueDate 2016-01-13 -Paragraph 130 -Subparagraph f -Clause iii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=36&date=2016-03-30&anchor=para_130_f_iii&doctype=Standard -URIDate 2016-03-31 + Details
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