Retirement Benefits - Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Pension Plan [Member] | United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 19	$ 20
Interest cost	29	23
Expected return on plan assets	(83)	(77)
Settlement	0	1
Amortization of net loss	4	11
Amortization of prior service credit	0	0
Net periodic benefit (income)/cost	(31)	(22)
Pension Plan [Member] | United Kingdom [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	3	4
Interest cost	19	14
Expected return on plan assets	(39)	(43)
Settlement	0	0
Amortization of net loss	8	7
Amortization of prior service credit	(3)	(4)
Net periodic benefit (income)/cost	(12)	(22)
Pension Plan [Member] | Other Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	6	6
Interest cost	4	3
Expected return on plan assets	(10)	(9)
Settlement	0	0
Amortization of net loss	1	1
Amortization of prior service credit	0	0
Net periodic benefit (income)/cost	1	1
PRW [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	1	0
Expected return on plan assets	0	0
Settlement	0	0
Amortization of net loss	0	0
Amortization of prior service credit	(1)	(1)
Net periodic benefit (income)/cost	$ 0	$ (1)