Retirement benefits (Tables)

12 Months Ended

Dec. 31, 2022

Disclosure of defined benefit plans [abstract]

Defined Benefit Plan

	Defined benefit obligation									Fair value of plan assets									Net defined benefit obligation
	2022 $m			2021 $m			2020 $m			2022 $m			2021 $m			2020 $m			2022 $m			2021 $m			2020 $m
At 1 January		92			103			96			–			–			–			92			103			96
Recognised in profit or loss
Interest expense		2			2			3			–			–			–			2			2			3
		2			2			3			–			–			–			2			2			3
Recognised in other comprehensive income
Actuarial (gain)/loss arising from changes in:
Demographic assumptions		(1	)		(3	)		(3	)		–			–			–			(1	)		(3	)		(3	)
Financial assumptions		(22	)		(3	)		10			–			–			–			(22	)		(3	)		10
Experience adjustments		2			(1	)		1			–			–			–			2			(1	)		1
Re-measurement (gain)/loss		(21	)		(7	)		8			–			–			–			(21	)		(7	)		8
Exchange adjustments		(2	)		(1	)		2			–			–			–			(2	)		(1	)		2
		(23	)		(8	)		10			–			–			–			(23	)		(8	)		10
Other
Group contributions		–			–			–			(5	)		(5	)		(6	)		(5	)		(5	)		(6	)
Benefits paid		(5	)		(5	)		(6	)		5			5			6			–			–			–
		(5	)		(5	)		(6	)		–			–			–			(5	)		(5	)		(6	)
At 31 December		66			92			103			–			–			–			66			92			103
Comprising:
UK plan		18			30			31			–			–			–			18			30			31
US plans		35			45			50			–			–			–			35			45			50
US post-retirement plan		13			17			22			–			–			–			13			17			22
		66			92			103			–			–			–			66			92			103

Summary of Principal Financial Assumptions Used to Determine Benefit Obligations

The principal financial assumptions used by the actuaries to determine the defined benefit obligations are:

	2022 %		2021 %		2020 %
UK plan only:
Pension increases		3.2		3.4		3.0
Inflation rate		3.2		3.4		3.0
Discount rate:
UK plan		5.0		1.8		1.4
US plans		4.9		2.4		1.9
US post-retirement plan		4.9		2.4		2.0
US healthcare cost trend rate assumed for the next year:
Pre-65 (ultimate rate reached in 2032)		6.9		6.2		6.4
Post-65 (ultimate rate reached in 2032)		7.3		6.5		6.8
Ultimate rate that the cost rate trends to		4.5		4.5		4.5

Defined Benefit Plans - Life Expectancy Assumptions at Retirement Age

The assumptions applied to the UK plan and US plans for life expectancy at retirement age are as follows:

		UK						US
		2022 years		2021 years		2020 years		2022 years		2021 years		2020 years
Current pensioners at 65a	– male		24		24		24		22		22		22
	– female		26		26		26		23		23		23
Future pensioners at 65b	– male		25		25		25		23		23		23
	– female		27		28		28		25		25		24

a  Relates to assumptions based on longevity following retirement at the end of the reporting period.

b  Relates to assumptions based on longevity relating to an employee retiring in 2042.

Defined Benefit Plans - Sensitivity Analysis of Actuarial Assumptions

The sensitivity analysis below relates to the increase/(decrease) in the benefit obligation and is based on extrapolating reasonable changes in these assumptions, using year-end conditions and assuming no interdependency between the assumptions:

		2022 $m			2021a $m
Discount rate	1% decrease		6.6			11.4
	1% increase		(5.4	)		(11.2	)
Inflation rate	0.25% decrease		(0.5	)		(1.2	)
	0.25% increase		0.6			1.3
Mortality rate	One-year increase		2.5			5.1
Healthcare costs trend rate	1% decrease		(0.8	)		(1.2	)
	1% increase		0.8			1.3

a  2021 sensitivities have been re-presented to show the effect of a 1% change in discount rate, consistent with 2022.

Summary of Estimated Future Benefit Payments

	2022 $m		2021 $m
Within one year		5		5
Between one and five years		20		21
More than five years		89		96
		114		122

	2022 years		2021 years
UK plan		14.0		19.0
US plans		7.6		9.0
US post-retirement plan		8.0		9.4