Employee Benefit Plans (Target and Actual Asset Allocation for Pension Plan by Asset Category) (Details) - Employee Pension Plans [Member]	Dec. 31, 2017	Dec. 31, 2016
Pension Plan Assets
Target asset allocation (as a percent)	100.00%
Actual asset allocation (as a percent)	100.00%	100.00%
Cash [Member]
Pension Plan Assets
Target asset allocation (as a percent)	5.00%
Actual asset allocation (as a percent)	3.00%	4.00%
Domestic Equity Funds
Pension Plan Assets
Target asset allocation (as a percent)	37.00%
Actual asset allocation (as a percent)	41.00%	47.00%
International Equity Funds
Pension Plan Assets
Target asset allocation (as a percent)	28.00%
Actual asset allocation (as a percent)	31.00%	28.00%
Fixed Income Funds
Pension Plan Assets
Target asset allocation (as a percent)	30.00%
Actual asset allocation (as a percent)	25.00%	21.00%