Provision for post-employment benefits - Movement in Pension Plan Assets (Detail) - GBP (£) £ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of net defined benefit (liability) asset
Fair value of plan assets at beginning of year	£ (206.3)	£ (276.5)
Employer contributions	(44.9)	(68.2)	£ (43.7)
Fair value of plan assets at end of year	(184.3)	(206.3)	(276.5)
Plan assets [member]
Disclosure of net defined benefit (liability) asset
Fair value of plan assets at beginning of year	930.0	934.2	814.2
Interest income on plan assets	26.3	26.6	30.5
Return on plan assets (excluding interest income)	(43.9)	13.4	66.3
Employer contributions	44.9	68.2	43.7
Benefits paid	(75.6)	(79.7)	(92.4)
Gain/(loss) due to exchange rate movements	23.0	(28.7)	78.8
Settlement payments	(70.4)	(1.2)	(4.8)
Administrative expenses	(3.4)	(3.1)	(2.2)
Other	9.7	0.3	0.1
Fair value of plan assets at end of year	840.6	930.0	934.2
Actual return on plan assets	£ (17.6)	£ 40.0	£ 96.8

The decrease (increase) in net defined benefit liability (asset) resulting from contributions to a defined benefit plan by the employer. [Refer: Net defined benefit liability (asset); Defined benefit plans [member]]

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Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

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No definition available.

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The increase (decrease) in the net defined benefit liability (asset) resulting from changes in foreign exchange rates. [Refer: Net defined benefit liability (asset)]

+ References

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- Definition

The increase (decrease) in the net defined benefit liability (asset) resulting from changes that the entity does not separately disclose in the same statement or note. [Refer: Net defined benefit liability (asset)]

+ References

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- Definition

The amount of deficit or surplus in a defined benefit plan, adjusted for any effect of limiting a net defined benefit asset to the asset ceiling. [Refer: Defined benefit plans [member]]

+ References

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The decrease (increase) in the net defined benefit liability (asset) resulting from payments from the plan. [Refer: Net defined benefit liability (asset)]

+ References

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The decrease (increase) in the net defined benefit liability (asset) resulting from payments from the plan in respect of settlements. [Refer: Gains (losses) arising from settlements, net defined benefit liability (asset); Net defined benefit liability (asset); Defined benefit plans [member]]

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The decrease (increase) in the net defined benefit liability (asset) resulting from the return on plan assets, excluding amounts included in interest income or expense. The return on plans assets is interest, dividends and other revenue derived from the plan assets, together with realised and unrealised gains or losses on the plan assets, less any costs of managing plan assets and less any tax payable by the plan itself, other than tax included in the actuarial assumptions used to measure the present value of the defined benefit obligation. [Refer: Plan assets [member]; Net defined benefit liability (asset); Actuarial assumptions [member]; Interest expense (income), net defined benefit liability (asset)]

+ References

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Actual return on plan assets

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Administrative Expense Net Defined Benefit Liability Asset.

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Interest income on plan assets.

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