Employee Benefits - Amounts recognized in Accumulated other comprehensive loss that have not yet been recognized (Details) - Pension Plan - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
U.K.
Amounts recognized in Accumulated other comprehensive loss unrecognized as components of net periodic benefit cost
Net loss	$ 1,870	$ 1,726
Prior service cost (income)	39	35
Net amount recognized	1,909	1,761
Other
Amounts recognized in Accumulated other comprehensive loss unrecognized as components of net periodic benefit cost
Net loss	436	443
Prior service cost (income)	(5)	(6)
Net amount recognized	431	437
U.S.
Amounts recognized in Accumulated other comprehensive loss unrecognized as components of net periodic benefit cost
Net loss	1,319	1,305
Prior service cost (income)	0	0
Net amount recognized	$ 1,319	$ 1,305