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Retirement Plans and Other Post-Retirement Benefits - Schedule of Fair Value of Benefit Plan Assets (Detail) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | $ 333.2 | $ 372.8
Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | 41.8 | 65.2
Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | 291.4 | 307.6
Fixed Income [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | 330.9 | 161.1
Fixed Income [Member] | Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | 41.8 | 13.3
Fixed Income [Member] | Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | 289.1 | 147.8
Cash and Equivalents [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | 2.3 | 6.7
Cash and Equivalents [Member] | Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets |  | 0.1
Cash and Equivalents [Member] | Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | $ 2.3 | 6.6
Large Cap [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets |  | 119.0
Large Cap [Member] | Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets |  | 6.9
Large Cap [Member] | Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets |  | 112.1
Small and Mid Cap [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets |  | 25.6
Small and Mid Cap [Member] | Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets |  | 25.6
International Equity [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets |  | 45.1
International Equity [Member] | Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets |  | 4.0
International Equity [Member] | Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets |  | 41.1
Real Estate Investment Trusts (REIT) [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets |  | 15.3
Real Estate Investment Trusts (REIT) [Member] | Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets |  | $ 15.3

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