Retirement Benefits - Net Periodic Benefit Cost (Details) - Pension Plan [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 11	$ 14
Interest cost	49	49
Expected return on plan assets	(76)	(76)
Amortization of net loss	9	3
Amortization of prior service credit	0	0
Net periodic benefit (income)/cost	(7)	(10)
United Kingdom [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1
Interest cost	28	29
Expected return on plan assets	(39)	(39)
Amortization of net loss	14	12
Amortization of prior service credit	(3)	(3)
Net periodic benefit (income)/cost	1	0
Other Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	3
Interest cost	7	7
Expected return on plan assets	(10)	(9)
Amortization of net loss	0	0
Amortization of prior service credit	0	0
Net periodic benefit (income)/cost	$ 1	$ 1