Retirement Plans (Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Special termination benefits	$ 44		$ 5
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	82	$ 90	97
Interest cost on projected benefit obligation	130	125	127
Expected return on plan assets	(172)	(192)	(186)
Amortization of unrecognized gain (loss)	58	24	30
Net periodic benefit cost	98	47	68
Pension settlement costs	57	41	83
Special termination benefits	38		5
Total benefit cost	193	88	156
Postretirement Benefits Other Than Pensions (OPEB) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	20	21	21
Interest cost on projected benefit obligation	41	38	40
Amortization of prior service credit	(11)	(9)	(9)
Amortization of unrecognized gain (loss)	(4)	3
Net periodic benefit cost	46	53	52
Special termination benefits	6
Total benefit cost	$ 52	$ 53	$ 52