Retirement Plans (Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension settlement costs				$ 25
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 21	$ 24	$ 42	48
Interest cost on projected benefit obligation	32	30	65	60
Expected return on plan assets	(43)	(48)	(86)	(98)
Amortization of unrecognized (gain) loss	14	6	28	13
Net periodic pension benefit cost	24	12	49	23
Pension settlement costs		25		25
Net periodic benefit cost	24	37	49	48
Postretirement Benefits Other Than Pensions (OPEB) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	5	6	10	11
Interest cost on projected benefit obligation	11	10	21	19
Amortization of prior service cost (credit)	(3)	(3)	(4)	(5)
Amortization of unrecognized (gain) loss			(2)	1
Net periodic benefit cost	$ 13	$ 13	$ 25	$ 26