Retirement Benefits (Unaudited) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Components of Net Periodic Benefit Cost
Net periodic benefit cost (benefit)			$ (818)	$ (612)
Defined contribution plan, employer contributions	$ 99	$ 116	476	472
Pension Benefits
Components of Net Periodic Benefit Cost
Service cost	104	102	311	306
Interest cost	263	307	790	920
Expected return on plan assets	(627)	(594)	(1,884)	(1,782)
Amortization of prior service credit	(3)	(15)	(7)	(45)
Net periodic benefit cost (benefit)	(263)	(200)	(790)	(601)
Defined benefit plan, contributions by Employer	26	24	79	70
OPB
Components of Net Periodic Benefit Cost
Service cost	4	4	12	13
Interest cost	13	17	40	50
Expected return on plan assets	(26)	(26)	(79)	(77)
Amortization of prior service credit	0	1	(1)	3
Net periodic benefit cost (benefit)	(9)	(4)	(28)	(11)
Defined benefit plan, contributions by Employer	$ 8	$ 7	$ 29	$ 30