Savings Plans, Pension Plans and Other Postretirement Employee Benefits (Actual Plan Asset Allocations of the Pension Benefit Plans' Assets) (Details) - Pension Plans [Member]	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan, Actual Plan Asset Allocations	100.00%	100.00%
Domestic Equity Securities [Member]
Defined Benefit Plan, Actual Plan Asset Allocations	37.00%	36.00%
Fixed income [Member]
Defined Benefit Plan, Actual Plan Asset Allocations	47.00%	48.00%
Other notes [Member]
Defined Benefit Plan, Actual Plan Asset Allocations	16.00%	16.00%