Retirement Benefits (Unaudited) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Defined Contribution Plan [Abstract]
Defined contribution plan, employer contributions	$ 256	$ 191
Pension Benefits
Components of Net Periodic Benefit Cost
Service cost	102	92
Interest cost	307	340
Expected return on plan assets	(594)	(525)
Amortization of prior service credit	(15)	(15)
Net periodic benefit cost (benefit)	(200)	(108)
Defined benefit plan, contributions by Employer	20	23
OPB
Components of Net Periodic Benefit Cost
Service cost	4	4
Interest cost	17	20
Expected return on plan assets	(26)	(23)
Amortization of prior service credit	1	(1)
Net periodic benefit cost (benefit)	(4)	0
Defined benefit plan, contributions by Employer	$ 12	$ 12