Retirement Benefits (Unaudited) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Components of Net Periodic Benefit Cost
Defined contribution plan, employer contributions	$ 266	$ 256
Pension Benefits
Components of Net Periodic Benefit Cost
Service cost	104	102
Interest cost	263	307
Expected return on plan assets	(628)	(594)
Amortization of prior service credit	(2)	(15)
Net periodic benefit cost (benefit)	(263)	(200)
Defined benefit plan, contributions by Employer	27	20
OPB
Components of Net Periodic Benefit Cost
Service cost	4	4
Interest cost	13	17
Expected return on plan assets	(26)	(26)
Amortization of prior service credit	0	1
Net periodic benefit cost (benefit)	(9)	(4)
Defined benefit plan, contributions by Employer	$ 11	$ 12