Retirement Benefits (Unaudited) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Components of Net Periodic Benefit Cost
Defined contribution plan, employer contributions	$ 116	$ 98	$ 472	$ 377
Pension Benefits
Components of Net Periodic Benefit Cost
Service cost	102	92	306	276
Interest cost	307	340	920	1,020
Expected return on plan assets	(594)	(525)	(1,782)	(1,576)
Amortization of prior service credit	(15)	(15)	(45)	(44)
Net periodic benefit cost (benefit)	(200)	(108)	(601)	(324)
Defined benefit plan, contributions by Employer	24	18	70	64
OPB
Components of Net Periodic Benefit Cost
Service cost	4	4	13	12
Interest cost	17	20	50	60
Expected return on plan assets	(26)	(23)	(77)	(69)
Amortization of prior service credit	1	(1)	3	(2)
Net periodic benefit cost (benefit)	(4)	0	(11)	1
Defined benefit plan, contributions by Employer	$ 7	$ 10	$ 30	$ 34