Retirement Benefits - Net Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Pension Benefits
Defined Contribution Plan Disclosure [Line Items]
Service cost	$ 33	$ 36
Interest cost	70	59
Expected return on assets	(137)	(123)
Prior service cost (credit)	0	0
Actuarial loss	38	50
Net periodic benefit cost	4	22
Non-service costs		(14)
OPEB
Defined Contribution Plan Disclosure [Line Items]
Service cost	6	7
Interest cost	13	11
Expected return on assets	(14)	(15)
Prior service cost (credit)	(2)	(2)
Actuarial loss	0	3
Net periodic benefit cost	$ 3	4
Non-service costs		$ (3)