Pensions and Other Postretirement Benefits (Net Periodic Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 6	$ 8
Interest cost	26	24
Expected return on plan assets	(35)	(38)
Defined Benefit Plan, Amortization of Gain (Loss)	15	16
Amortization of prior service credit	0	0
Net periodic benefit cost	12	10
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	2
Interest cost	6	6
Expected return on plan assets	0	0
Defined Benefit Plan, Amortization of Gain (Loss)	2	5
Amortization of prior service credit	(14)	(15)
Net periodic benefit cost	$ (4)	$ (2)