Investments - Summary of Investments - Asanko preference shares (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021
Disclosure of detailed information about financial instruments [abstract]
Fair value at beginning of the year	$ 94.5	$ 92.6
Redemption of preference shares	0.0	(5.0)
Net change in fair value (recognised in OCI)	34.2	(6.9)
Fair value at end of the year	$ 60.3	$ 94.5
Nominal discount rate	16.70%	9.00%

The gains (losses) recognised in other comprehensive income on financial assets measured at fair value through other comprehensive income applying paragraph 4.1.2A of IFRS 9, before tax, before reclassification adjustments. [Refer: Financial assets measured at fair value through other comprehensive income; Other comprehensive income]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
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