Retirement Benefits - Summary of Changes in Benefit Obligations and Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Net benefit obligation as of the beginning of year	$ 24,894	$ 22,868
Service cost	439	387	$ 357
Interest cost	641	757	883
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant	0	0
Actuarial (gain) loss(a)	(630)	2,217
Plan amendments	0	0
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement	(88)	(45)
Defined Benefit Plan, Benefit Obligation, Benefits Paid	(1,410)	(1,290)
Net benefit obligation as of the end of year	23,846	24,894	22,868
Fair value of net plan assets as of the beginning of year	20,344	18,590
Actual return on plan assets	1,407	2,547
Employer contributions	574	542
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant	0	0
Defined Benefit Plan, Plan Assets, Benefits Paid	(1,410)	(1,290)
Defined Benefit Plan, Plan Assets, Payment for Settlement	(88)	(45)
Fair value of net plan assets as of the end of year	20,827	20,344	18,590
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	4,604	4,658
Service cost	80	90	93
Interest cost	114	154	188
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant	50	49
Actuarial (gain) loss(a)	(223)	49
Plan amendments	0	(111)
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement	(5)	(5)
Defined Benefit Plan, Benefit Obligation, Benefits Paid	(292)	(280)
Net benefit obligation as of the end of year	4,328	4,604	4,658
Fair value of net plan assets as of the beginning of year	2,554	2,541
Actual return on plan assets	203	190
Employer contributions	91	59
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant	50	49
Defined Benefit Plan, Plan Assets, Benefits Paid	(292)	(280)
Defined Benefit Plan, Plan Assets, Payment for Settlement	(5)	(5)
Fair value of net plan assets as of the end of year	$ 2,601	$ 2,554	$ 2,541