Retirement Benefits - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Amortization of:
Net periodic benefit cost	$ 91	$ 53	$ 13
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	439	387	357
Interest cost	641	757	883
Expected return on assets	(1,336)	(1,270)	(1,225)
Amortization of:
Prior service cost (credit)	3	4	0
Actuarial loss	598	512	414
Curtailment benefits	0	0	0
Settlement and other charges	27	14	17
Contractual termination benefits	0	0	1
Net periodic benefit cost	372	404	447
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	80	90	93
Interest cost	114	154	188
Expected return on assets	(158)	(163)	(153)
Amortization of:
Prior service cost (credit)	(34)	(124)	(179)
Actuarial loss	37	49	45
Curtailment benefits	0	(1)	0
Settlement and other charges	1	1	1
Contractual termination benefits	0	0	0
Net periodic benefit cost	$ 40	$ 6	$ (5)