Retirement Plans (Plan Asset Investment Allocation Percentage) (Details) - Pension Plan	Dec. 31, 2017	Dec. 31, 2016
UNITED STATES
Asset Category
Percentage of plan assets	100.00%	100.00%
UNITED STATES | Cash and cash equivalents
Asset Category
Percentage of plan assets	2.00%	5.00%
UNITED STATES | Cash and cash equivalents | Minimum
Asset Category
Targets percentage of plan assets	0.00%
UNITED STATES | Cash and cash equivalents | Maximum
Asset Category
Targets percentage of plan assets	10.00%
UNITED STATES | Total fixed income funds
Asset Category
Percentage of plan assets	32.00%	33.00%
UNITED STATES | Total fixed income funds | Minimum
Asset Category
Targets percentage of plan assets	25.00%
UNITED STATES | Total fixed income funds | Maximum
Asset Category
Targets percentage of plan assets	50.00%
UNITED STATES | Total mutual funds and equities
Asset Category
Percentage of plan assets	66.00%	62.00%
UNITED STATES | Total mutual funds and equities | Minimum
Asset Category
Targets percentage of plan assets	50.00%
UNITED STATES | Total mutual funds and equities | Maximum
Asset Category
Targets percentage of plan assets	70.00%
Foreign Plan | Cash and cash equivalents | Maximum
Asset Category
Targets percentage of plan assets	100.00%
Foreign Plan | Equity securities | Maximum
Asset Category
Targets percentage of plan assets	100.00%
Foreign Plan | Commercial property | Maximum
Asset Category
Targets percentage of plan assets	50.00%
Foreign Plan | U.K. Government securities | Maximum
Asset Category
Targets percentage of plan assets	50.00%