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Benefit Plans (Allocation of Plan Assets) (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2016 | Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Fair Value of Plan Assets | $ 192.4 | $ 188.9
Weighted average asset allocations | 100.00% | 100.00%
Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Fair Value of Plan Assets |  | $ 188.3
Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Fair Value of Plan Assets |  | 0.6
Cash [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Fair Value of Plan Assets | $ 10.0 | 0.6
Cash [Member] | Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Fair Value of Plan Assets | $ 10.0 | $ 0.6
Equity Securities [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Weighted average asset allocations | 60.00% | 62.00%
Target allocation | 65.00% |
Allocation range minimum | 60.00% |
Allocation range maximum | 70.00% |
Indexed Mutual Funds [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Fair Value of Plan Assets | $ 8.9 | $ 79.2
Indexed Mutual Funds [Member] | Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Fair Value of Plan Assets | 8.9 | 79.2
International Mutual Funds [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Fair Value of Plan Assets | 3.0 | 37.7
International Mutual Funds [Member] | Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Fair Value of Plan Assets | $ 3.0 | $ 37.7
Debt Securities [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Weighted average asset allocations | 30.00% | 35.00%
Target allocation | 35.00% |
Allocation range minimum | 30.00% |
Allocation range maximum | 40.00% |
Other [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Weighted average asset allocations | 10.00% | 3.00%
Target allocation | 0.00% |
Allocation range minimum | 0.00% |
Allocation range maximum | 5.00% |
Mutual Funds [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Fair Value of Plan Assets | $ 9.2 | $ 63.0
Mutual Funds [Member] | Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Fair Value of Plan Assets | 9.2 | 63.0
Insurance Contract [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Fair Value of Plan Assets | 0.5 | 0.6
Insurance Contract [Member] | Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Fair Value of Plan Assets | 0.5 | 0.6
Balanced Mutual Fund [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Fair Value of Plan Assets | 6.3 | 7.8
Balanced Mutual Fund [Member] | Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Fair Value of Plan Assets | 6.3 | $ 7.8
Pension Plan Assets In The Fair Value Hierarchy [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Fair Value of Plan Assets | 37.9 |
Pension Plan Assets In The Fair Value Hierarchy [Member] | Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Fair Value of Plan Assets | 37.4 |
Pension Plan Assets In The Fair Value Hierarchy [Member] | Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Fair Value of Plan Assets | 0.5 |
Pension plan assets measured at NAV [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Fair Value of Plan Assets | $ 154.5 |

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