Retirement Benefits - Change in Benefit Obligation and Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Change in Plan Assets
Fair value of plan assets, beginning of year	$ 7,402
Fair value of plan assets, end of year	7,545	$ 7,402
Pension benefits assets	588	827
Non-current liability for pension benefits	(563)	(480)
Pension Plan [Member] | United States [Member]
Change in Benefit Obligation
Benefit obligation, beginning of year	3,871	5,096
Service cost	56	77	$ 79
Interest cost	195	119	94
Employee contributions	17	16
Actuarial losses/(gains)	201	(1,186)
Settlements	(11)	(25)
Benefits paid	(230)	(226)
Other	(1)	0	1
Foreign currency changes	0	0
Benefit obligation, end of year	4,098	3,871	5,096
Change in Plan Assets
Fair value of plan assets, beginning of year	3,823	4,710
Actual return on plan assets	173	(694)
Employer contributions	31	42
Employee contributions	17	16
Settlements	(11)	(25)
Benefits paid	(230)	(226)
Other	0	0
Foreign currency changes	0	0
Fair value of plan assets, end of year	3,803	3,823	4,710
Funded status at end of year	(295)	(48)
Accumulated Benefit Obligation	4,098	3,871
Pension benefits assets	0	179
Current liability for pension benefits	(24)	(26)
Non-current liability for pension benefits	(271)	(201)
Components on the Consolidated Balance Sheet	(295)	(48)
Pension Plan [Member] | United Kingdom [Member]
Change in Benefit Obligation
Benefit obligation, beginning of year	2,435	4,369
Service cost	6	12	17
Interest cost	120	70	56
Employee contributions	0	0
Actuarial losses/(gains)	(32)	(1,434)
Settlements	0	(5)
Benefits paid	(116)	(130)
Other	0	0
Foreign currency changes	145	(447)
Benefit obligation, end of year	2,558	2,435	4,369
Change in Plan Assets
Fair value of plan assets, beginning of year	2,999	5,266
Actual return on plan assets	(3)	(1,622)
Employer contributions	13	33
Employee contributions	0	0
Settlements	0	(5)
Benefits paid	(116)	(130)
Other	0	0
Foreign currency changes	176	(543)
Fair value of plan assets, end of year	3,069	2,999	5,266
Funded status at end of year	511	564
Accumulated Benefit Obligation	2,558	2,435
Pension benefits assets	516	569
Current liability for pension benefits	(1)	0
Non-current liability for pension benefits	(4)	(5)
Components on the Consolidated Balance Sheet	511	564
Pension Plan [Member] | Other Foreign Plans [Member]
Change in Benefit Obligation
Benefit obligation, beginning of year	655	922
Service cost	14	22	24
Interest cost	28	15	12
Employee contributions	1	1
Actuarial losses/(gains)	72	(221)
Settlements	(2)	(2)
Benefits paid	(35)	(30)
Other	3	2
Foreign currency changes	26	(54)
Benefit obligation, end of year	762	655	922
Change in Plan Assets
Fair value of plan assets, beginning of year	580	739
Actual return on plan assets	67	(124)
Employer contributions	36	38
Employee contributions	1	1
Settlements	(2)	(2)
Benefits paid	(35)	(30)
Other	3	2
Foreign currency changes	23	(44)
Fair value of plan assets, end of year	673	580	$ 739
Funded status at end of year	(89)	(75)
Accumulated Benefit Obligation	733	629
Pension benefits assets	52	57
Current liability for pension benefits	(5)	(5)
Non-current liability for pension benefits	(136)	(127)
Components on the Consolidated Balance Sheet	$ (89)	$ (75)