Retirement Plans (Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Special termination benefits		$ 5	$ 26
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 90	97	88
Interest cost on projected benefit obligation	125	127	122
Expected return on plan assets	(192)	(186)	(168)
Amortization of unrecognized loss	24	30	40
Net periodic benefit cost	47	68	82
Pension settlement costs	41	83
Special termination benefits		5	23
Total Disclosed Benefit Cost	88	156	105
Postretirement Benefits Other Than Pensions (OPEB) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	21	21	19
Interest cost on projected benefit obligation	38	40	37
Amortization of prior service (credit) costs	(9)	(9)	(9)
Amortization of unrecognized loss	3		1
Net periodic benefit cost	53	52	48
Special termination benefits			3
Total Disclosed Benefit Cost	$ 53	$ 52	$ 51