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Retirement benefits - Defined Benefit Plans - Sensitivity Analysis of Actuarial Assumptions (Detail) $ in Millions | Dec. 31, 2018 USD ($)
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United Kingdom [member] | 0.25% decrease [member] | Increase/ (decrease) In liabilities [member] | Pensions increases [member] |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |
Decrease in actuarial assumption | $ (1.0)
United Kingdom [member] | 0.25% decrease [member] | Increase/ (decrease) In liabilities [member] | Discount rate [member] |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |
Decrease in actuarial assumption | 1.0
United Kingdom [member] | 0.25% decrease [member] | Increase/ (decrease) In liabilities [member] | Inflation rate [member] |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |
Decrease in actuarial assumption | (1.0)
United Kingdom [member] | 0.25% increase [member] | Higher/(lower) pension cost [member] | Pensions increases [member] |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |
Increase in actuarial assumption | 0.1
United Kingdom [member] | 0.25% increase [member] | Higher/(lower) pension cost [member] | Discount rate [member] |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |
Increase in actuarial assumption | 0.1
United Kingdom [member] | 0.25% increase [member] | Higher/(lower) pension cost [member] | Inflation rate [member] |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |
Increase in actuarial assumption | 0.1
United Kingdom [member] | 0.25% increase [member] | Increase/ (decrease) In liabilities [member] | Pensions increases [member] |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |
Decrease in actuarial assumption | 1.0
United Kingdom [member] | 0.25% increase [member] | Increase/ (decrease) In liabilities [member] | Discount rate [member] |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |
Decrease in actuarial assumption | (1.0)
United Kingdom [member] | 0.25% increase [member] | Increase/ (decrease) In liabilities [member] | Inflation rate [member] |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |
Decrease in actuarial assumption | 1.0
United Kingdom [member] | One year increase [member] | Higher/(lower) pension cost [member] | Mortality rate [member] |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |
Increase in actuarial assumption | 0.1
United Kingdom [member] | One year increase [member] | Increase/ (decrease) In liabilities [member] | Mortality rate [member] |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |
Decrease in actuarial assumption | 0.6
United States [member] | 0.25% decrease [member] | Higher/(lower) pension cost [member] | Discount rate [member] |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |
Decrease in actuarial assumption | (0.1)
United States [member] | 0.25% decrease [member] | Increase/ (decrease) In liabilities [member] | Discount rate [member] |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |
Decrease in actuarial assumption | 1.6
United States [member] | 0.25% increase [member] | Higher/(lower) pension cost [member] | Discount rate [member] |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |
Increase in actuarial assumption | 0.1
United States [member] | 0.25% increase [member] | Increase/ (decrease) In liabilities [member] | Discount rate [member] |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |
Decrease in actuarial assumption | (1.5)
United States [member] | One year increase [member] | Higher/(lower) pension cost [member] | Mortality rate [member] |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |
Increase in actuarial assumption | 0.1
United States [member] | One year increase [member] | Increase/ (decrease) In liabilities [member] | Mortality rate [member] |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |
Decrease in actuarial assumption | $ 3.3

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