Retirement benefits (Tables)

12 Months Ended

Dec. 31, 2021

Disclosure of defined benefit plans [abstract]

Defined Benefit Plan

	Defined benefit obligation									Fair value of plan assets									Net defined benefit obligation
	2021 $m			2020 $m			2019 $m			2021 $m			2020 $m			2019 $m			2021 $m			2020 $m			2019 $m
At 1 January		103			96			91			–			–			–			103			96			91
Recognised in profit or loss
Interest expense		2			3			3			–			–			–			2			3			3
		2			3			3			–			–			–			2			3			3
Recognised in other comprehensive income
Actuarial (gain)/loss arising from changes in:
Demographic assumptions		(3	)		(3	)		(1	)		–			–			–			(3	)		(3	)		(1	)
Financial assumptions		(3	)		10			9			–			–			–			(3	)		10			9
Experience adjustments		(1	)		1			(1	)		–			–			–			(1	)		1			(1	)
Re-measurement (gain)/loss		(7	)		8			7			–			–			–			(7	)		8			7
Exchange adjustments		(1	)		2			1			–			–			–			(1	)		2			1
		(8	)		10			8			–			–			–			(8	)		10			8
Other
Group contributions		–			–			–			(5	)		(6	)		(6	)		(5	)		(6	)		(6	)
Benefits paid		(5	)		(6	)		(6	)		5			6			6			–			–			–
		(5	)		(6	)		(6	)		–			–			–			(5	)		(6	)		(6	)
At 31 December		92			103			96			–			–			–			92			103			96
Comprising:
UK plan		30			31			26			–			–			–			30			31			26
US plans		45			50			48			–			–			–			45			50			48
US post-retirement plan		17			22			22			–			–			–			17			22			22
		92			103			96			–			–			–			92			103			96

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:

	2021		2020		2019
	%		%		%
UK plan only:
Pension increases		3.4		3.0		2.7
Inflation rate		3.4		3.0		2.7
Discount rate:
UK plan		1.8		1.4		2.1
US plans		2.4		1.9		2.9
US post-retirement plan		2.4		2.0		2.9
US healthcare cost trend rate assumed for the next year:
Pre-65 (ultimate rate reached in 2031)		6.2		6.4		6.7
Post-65 (ultimate rate reached in 2031)		6.5		6.8		7.1
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
		2021		2020		2019		2021		2020		2019
		Years		Years		Years		Years		Years		Years
Current pensioners at 65a	– male		24		24		24		22		22		21
	– female		26		26		26		23		23		23
Future pensioners at 65b	– male		25		25		25		23		23		22
	– female		28		28		28		25		24		24

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

b  Relates to assumptions based on longevity (in years) relating to an employee retiring in 2041.

Defined Benefit Plans - Sensitivity Analysis of Actuarial Assumptions

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

		2021 $m			2020 $m
Increase/(decrease) in liabilities
Discount rate	0.25% decrease		2.8			3.2
	0.25% increase		(2.8	)		(3.2	)
Inflation rate	0.25% decrease		(1.2	)		(1.4	)
	0.25% increase		1.3			1.4
Mortality rate	One-year increase		5.1			5.7
Healthcare costs trend rate	1% decrease		(1.2	)		(1.6	)
	1% increase		1.3			1.7

Summary of Estimated Future Benefit Payments

	2021 $m		2020 $m
Within one year		5		6
Between one and five years		21		22
More than five years		96		101
		122		129

	2021 Years	2020 Years
UK plan	19.0	19.0
US plans	9.0	9.3
US post-retirement plan	9.4	9.9