Pensions and Other Postretirement Benefits (Net Periodic Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Pension settlement charge	$ 0	$ 22
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	8	9
Interest cost	24	24
Expected return on plan assets	(38)	(34)
Amortization of actuarial losses	16	19
Amortization of prior service credit	0	0
Pension settlement charge	0
Net periodic pension/other postretirement benefit cost	10	40
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	2
Interest cost	6	7
Expected return on plan assets	0	0
Amortization of actuarial losses	5	5
Amortization of prior service credit	(15)	(13)
Pension settlement charge	0	0
Net periodic pension/other postretirement benefit cost	$ (2)	1
U.S. Non-qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Pension settlement charge		$ 22