Impairment - Narrative (Details) - GBP (£) £ in Millions	6 Months Ended
Jun. 30, 2026	Jun. 30, 2025
Disclosure of impairment loss and reversal of impairment loss [abstract]
Residual impairment and voluntary termination charge	£ 78	£ 70

It represents information about amount of residual impairment charges and voluntary termination.

No definition available.

Name:	lbk_ResidualValueAndVoluntaryImpairmentCharges
Namespace Prefix:	lbk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration