Retirement benefits (Tables)

12 Months Ended

Dec. 31, 2019

Disclosure of defined benefit plans [abstract]

Defined Benefit Plan

	Defined benefit obligation									Fair value of plan assets									Net defined benefit liability/(asset)
	2019			2018			2017			2019			2018			2017			2019			2018			2017
	$m			$m			$m			$m			$m			$m			$m			$m			$m
At 1 January		91			250			244			—			(152	)		(148	)		91			98			96
Recognised in profit or loss
Interest expense/(income)		3			6			9			—			(2	)		(5	)		3			4			4
Administration costs		—			—			—			—			—			1			—			—			1
Exceptional item: settlement loss		—			14			—			—			1			—			—			15			—
		3			20			9			—			(1	)		(4	)		3			19			5
Recognised in other comprehensive income
Actuarial loss/(gain) arising from changes in:
Demographic assumptions		(1	)		—			(1	)		—			—			—			(1	)		—			(1	)
Financial assumptions		9			(14	)		9			—			—			—			9			(14	)		9
Experience adjustments		(1	)		(3	)		2			—			—			—			(1	)		(3	)		2
Return on plan assets		—			—			—			—			8			(9	)		—			8			(9	)
Re-measurement loss/(gain)		7			(17	)		10			—			8			(9	)		7			(9	)		1
Exchange adjustments		1			(1	)		2			—			—			—			1			(1	)		2
		8			(18	)		12			—			8			(9	)		8			(10	)		3
Other
Company contributions		—			—			—			(6	)		(16	)		(6	)		(6	)		(16	)		(6	)
Benefits paid		(6	)		(11	)		(15	)		6			11			15			—			—			—
Settlement payments		—			(150	)		—			—			150			—			—			—			—
		(6	)		(161	)		(15	)		—			145			9			(6	)		(16	)		(6	)
At 31 December		96			91			250			—			—			(152	)		96			91			98
Comprising:
UK unfunded plan		26			24			29			—			—			—			26			24			29
US unfunded plans		48			45			51			—			—			—			48			45			51
US funded plan		—			—			146			—			—			(152	)		—			—			(6	)
US unfunded post-retirement plans		22			22			24			—			—			—			22			22			24
		96			91			250			—			—			(152	)		96			91			98

	Defined benefit obligation						Fair value of plan assets							Net defined benefit liability/(asset)
	2019		2018		2017		2019		2018			2017		2019		2018			2017
	$m		$m		$m		$m		$m			$m		$m		$m			$m
Movement in asset restriction
At 1 January		—		—		—		—		3			—		—		3			—
Recognised in other comprehensive income		—		—		—		—		(3	)		3		—		(3	)		3
At 31 December		—		—		—		—		—			3		—		—			3

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:

	2019		2018		2017
	%		%		%
UK plan only:
Pension increases		2.7		3.2		3.2
Inflation rate		2.7		3.2		3.2
Discount rate:
UK plan		2.1		3.0		2.6
US plans		2.9		3.9		3.3
US post-retirement plan		2.9		4.0		3.3
US Healthcare cost trend rate assumed for the next year:
Pre-65 (ultimate rate reached in 2028)		6.7		7.1		7.7
Post-65 (ultimate rate reached in 2028)		7.1		7.6		8.7
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 used for life expectancy at retirement age are as follows:

		UK						US
		2019		2018		2017		2019		2018		2017
		Years		Years		Years		Years		Years		Years
Current pensioners at 65a	– male		24		24		24		21		21		21
	– female		26		26		26		23		23		23
Future pensioners at 65b	– male		25		25		25		22		22		22
	– female		28		28		28		24		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 2037.

Summary of Estimated Future Benefit Payments

	2019		2018
	$m		$m
Within one year		6		5
Between one and five years		22		23
More than five years		36		38
		64		66

	2019		2018
	Years		Years
UK plan		18.0		19.5
US plans		9.3		9.2
US post-retirement plan		9.8		9.6