| Accumulated funds (deficit) [member] | Members funds [member] | Revaluation reserve [member] | Foreign currency translation reserve [member] | Capital reserve [member] | Other reserves [member] | Fair value adjustment reserve [member] | Total fund/equity and reserves attributable to owners [member] | Total fund/equity and reserves [member] | ||
| Statement of changes in fund/equity [abstract] | ||||||||||
| Balance at beginning of period | ||||||||||
| Impact of change in accounting policies | ||||||||||
| Other prior period adjustments | ||||||||||
| Balance at beginning of period, restated | ||||||||||
| Surplus (deficit) of income over expenditure | ||||||||||
| Total other comprehensive surplus (deficit) | ||||||||||
| Total comprehensive surplus (deficit) | ||||||||||
| Contributions by and distributions to owners [abstract] | ||||||||||
| Acquisition (dilution) of equity interest in subsidiaries | ||||||||||
| Reserve attributable to disposal group classified as held for sale | ||||||||||
| Dividend paid | ||||||||||
| Other transactions with owners | ||||||||||
| Total contributions by and distributions to owners | ||||||||||
| Total changes in fund/equity | ||||||||||
| Balance at end of period | ||||||||||