Retirement Benefits (Unaudited) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Components of Net Periodic Benefit Cost
Net periodic benefit cost (benefit)			$ (546)	$ (408)
Defined contribution plan, employer contributions	$ 111	$ 100	377	356
Pension Benefits
Components of Net Periodic Benefit Cost
Service cost	103	102	207	204
Interest cost	264	306	527	613
Expected return on plan assets	(629)	(594)	(1,257)	(1,188)
Amortization of prior service credit	(2)	(15)	(4)	(30)
Net periodic benefit cost (benefit)	(264)	(201)	(527)	(401)
Defined benefit plan, contributions by Employer	26	26	53	46
OPB
Components of Net Periodic Benefit Cost
Service cost	4	5	8	9
Interest cost	14	16	27	33
Expected return on plan assets	(27)	(25)	(53)	(51)
Amortization of prior service credit	(1)	1	(1)	2
Net periodic benefit cost (benefit)	(10)	(3)	(19)	(7)
Defined benefit plan, contributions by Employer	$ 10	$ 11	$ 21	$ 23