Retirement Benefits - Summary of Changes in Benefit Obligations and Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Net benefit obligation as of the beginning of year	$ 14,236	$ 14,861
Service cost	236	294	$ 251
Interest cost	439	406	476
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant	0	0
Actuarial (gain) loss(a)	(3,379)	(442)
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement	0	(23)
Defined Benefit Plan, Benefit Obligation, Benefits Paid	(855)	(860)
Net benefit obligation as of the end of year	10,677	14,236	14,861
Fair value of net plan assets as of the beginning of year	12,165	11,883
Actual return on plan assets	(2,359)	822
Employer contributions	570	343
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant	0	0
Defined Benefit Plan, Plan Assets, Benefits Paid	(855)	(860)
Defined Benefit Plan, Plan Assets, Payment for Settlement	0	(23)
Fair value of net plan assets as of the end of year	9,521	12,165	11,883
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Net benefit obligation as of the beginning of year	2,502	2,661
Service cost	41	51	56
Interest cost	76	69	93
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant	26	32
Actuarial (gain) loss(a)	(604)	(116)
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement	0	(5)
Defined Benefit Plan, Benefit Obligation, Benefits Paid	(157)	(190)
Net benefit obligation as of the end of year	1,884	2,502	2,661
Fair value of net plan assets as of the beginning of year	1,665	1,635
Actual return on plan assets	(225)	130
Employer contributions	42	63
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant	26	32
Defined Benefit Plan, Plan Assets, Benefits Paid	(157)	(190)
Defined Benefit Plan, Plan Assets, Payment for Settlement	0	(5)
Fair value of net plan assets as of the end of year	$ 1,351	$ 1,665	$ 1,635