Impairment loss is recognized immediately in P&L (unless the asset is carried at revalued amount) Thus, entries would be:
Dr Impairment losses a/c (P&L account)
Cr Asset account a/c (Balance sheet account)
If the asset is carried at revalued amount, impairment loss is treated as a reduction in revaluation gain.
Dr Revaluation surplus (B/S account)
Cr Asset account a/c (B/S account)
Reference: IAS 36 - Impairment of Assets