Benefit Obligations (Schedule of Amortization of Accumulated Other Comprehensive Income (Loss), Net Into Net Periodic Benefit Cost) (Details) $ in Millions	Dec. 31, 2017 USD ($)
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	$ 0
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	$ 0