Retirement Benefits (Details 8)	Dec. 31, 2017
Cash and Cash Equivalents [Member] | Minimum
Plan Asset Allocation Ranges (Table Amounts) [Abstract]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	0.00%
Cash and Cash Equivalents [Member] | Maximum
Plan Asset Allocation Ranges (Table Amounts) [Abstract]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	12.00%
U.S. Equity Securities [Member] | Minimum
Plan Asset Allocation Ranges (Table Amounts) [Abstract]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	15.00%
U.S. Equity Securities [Member] | Maximum
Plan Asset Allocation Ranges (Table Amounts) [Abstract]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	35.00%
International Equity Securities [Member] | Minimum
Plan Asset Allocation Ranges (Table Amounts) [Abstract]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	10.00%
International Equity Securities [Member] | Maximum
Plan Asset Allocation Ranges (Table Amounts) [Abstract]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	30.00%
Fixed income securities | Minimum
Plan Asset Allocation Ranges (Table Amounts) [Abstract]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	20.00%
Fixed income securities | Maximum
Plan Asset Allocation Ranges (Table Amounts) [Abstract]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	55.00%
Alternative investments | Minimum
Plan Asset Allocation Ranges (Table Amounts) [Abstract]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	8.00%
Alternative investments | Maximum
Plan Asset Allocation Ranges (Table Amounts) [Abstract]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	28.00%