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Pension Plans and Other Benefits - Plan Asset FV Measurements (Details) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Defined Benefit Plan Disclosure |  |  |
Fair value of asset |  | $ 701.2 | $ 793.2
Fair Value Inputs Level 1 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of asset |  | 12.0 | 14.7
Fair Value Inputs Level 2 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of asset |  | 687.2 | 775.5
Fair Value Inputs Level 3 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of asset |  | $ 2.0 | $ 3.0
Debt Security, Corporate, US [Member] |  |  |
Defined Benefit Plan Disclosure |  |  |
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage |  | 50.00% | 55.00%
US and Canada Government Debt Securities [Member] |  |  |
Defined Benefit Plan Disclosure |  |  |
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage |  | 44.00% | 42.00%
Canadian Equity Securities [Member] |  |  |
Defined Benefit Plan Disclosure |  |  |
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage |  | 18.00% | 25.00%
Cash And Cash Equivalents |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of asset |  | $ 12.0 | $ 14.7
Cash And Cash Equivalents | Fair Value Inputs Level 1 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of asset |  | 12.0 | 14.7
Cash And Cash Equivalents | Fair Value Inputs Level 2 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of asset |  | 0.0 | 0.0
Cash And Cash Equivalents | Fair Value Inputs Level 3 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of asset |  | 0.0 | 0.0
Equity Securities |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of asset | [1] | 172.9 | 327.7
Equity Securities | Fair Value Inputs Level 1 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of asset | [1] | 0.0 | 0.0
Equity Securities | Fair Value Inputs Level 2 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of asset | [1] | 172.9 | 327.7
Equity Securities | Fair Value Inputs Level 3 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of asset | [1] | 0.0 | 0.0
Fixed Income Securities |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of asset | [2] | 514.3 | 447.8
Fixed Income Securities | Fair Value Inputs Level 1 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of asset | [2] | 0.0 | 0.0
Fixed Income Securities | Fair Value Inputs Level 2 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of asset | [2] | 514.3 | 447.8
Fixed Income Securities | Fair Value Inputs Level 3 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of asset | [2] | 0.0 | 0.0
Private Equity Funds |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of asset |  | 2.0 | 3.0
Private Equity Funds | Fair Value Inputs Level 1 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of asset |  | 0.0 | 0.0
Private Equity Funds | Fair Value Inputs Level 2 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of asset |  | 0.0 | 0.0
Private Equity Funds | Fair Value Inputs Level 3 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of asset |  | $ 2.0 | $ 3.0
Other Foreign [Member] |  |  |
Defined Benefit Plan Disclosure |  |  |
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage |  | 43.00% | 30.00%
U.S. Government Bonds |  |  |
Defined Benefit Plan Disclosure |  |  |
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage |  | 39.00% | 45.00%
Debt Security, Corporate, Non-US [Member] |  |  |
Defined Benefit Plan Disclosure |  |  |
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage |  | 6.00% | 3.00%
[1] | This class, which includes several funds, was invested approximately 39% in U.S. equity securities, 18% in Canadian equity securities, and 43% in international equity securities as of December 31, 2018, and 45% in U.S. equity securities, 25% in Canadian equity securities, and 30% in international equity securities as of December 31, 2017.
[2] | This class, which includes several funds, was invested approximately 50% in corporate debt securities, 44% in governmental securities in the U.S. and Canada, and 6% in foreign entity debt securities as of December 31, 2018, and 55% in corporate debt securities, 42% in governmental securities in the U.S. and Canada, and 3% in foreign entity debt securities as of December 31, 2017.

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