Retirement Plans (Schedule of Annual Pension and Other Post-Retirement Benefit Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 111	$ 180	$ 168
Interest cost	600	532	453
Expected return on plan assets	(911)	(856)	(679)
Recognized net actuarial loss (gain)	326	359	362
Amortization of prior service credit	(19)	(46)	(66)
Annual benefit (credit) cost	107	169	238
Other Post-retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	8	10	9
Interest cost	35	33	30
Expected return on plan assets	(36)	(40)	(34)
Recognized net actuarial loss (gain)	(8)	(4)	(4)
Amortization of prior service credit	(3)	(4)	(3)
Annual benefit (credit) cost	$ (4)	$ (5)	$ (2)