Retirement Plans (Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension settlement costs	$ 103
Net periodic benefit cost	125	$ 25
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	25	21
Interest cost on projected benefit obligation	30	33
Expected return on plan assets	(50)	(43)
Amortization of unrecognized (gain) loss	17	14
Net periodic pension benefit cost	22	25
Pension settlement costs	103
Postretirement Costs [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	5	5
Interest cost on projected benefit obligation	8	10
Amortization of prior service cost (credit)	(8)	(1)
Amortization of unrecognized (gain) loss	2	(2)
Net periodic benefit cost	$ 7	$ 12