Fair Value of Pension Assets (Detail) (Pension Benefits [Member], USD $)
In Millions, unless otherwise specified |
Dec. 31, 2012
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Dec. 31, 2011
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Dec. 31, 2010
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Defined Benefit Plan Disclosure [Line Items] | ||||||||||||||
Fair value of plan assets | $ 548.0 | $ 583.0 | $ 569.9 | |||||||||||
Large-Cap Equity
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Defined Benefit Plan Disclosure [Line Items] | ||||||||||||||
Fair value of plan assets | 94.5 | [1] | ||||||||||||
Small- and Mid-Cap Equity
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Defined Benefit Plan Disclosure [Line Items] | ||||||||||||||
Fair value of plan assets | 19.6 | [1] | ||||||||||||
International Equity
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Defined Benefit Plan Disclosure [Line Items] | ||||||||||||||
Fair value of plan assets | 109.3 | [1],[2] | ||||||||||||
Fixed Income
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Defined Benefit Plan Disclosure [Line Items] | ||||||||||||||
Fair value of plan assets | 162.4 | [1],[2] | ||||||||||||
Private Equity
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Defined Benefit Plan Disclosure [Line Items] | ||||||||||||||
Fair value of plan assets | 36.0 | [3] | ||||||||||||
Hedge Funds
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Defined Benefit Plan Disclosure [Line Items] | ||||||||||||||
Fair value of plan assets | 89.1 | [4] | ||||||||||||
Real Assets
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Defined Benefit Plan Disclosure [Line Items] | ||||||||||||||
Fair value of plan assets | 29.3 | [1],[5] | ||||||||||||
Cash
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Defined Benefit Plan Disclosure [Line Items] | ||||||||||||||
Fair value of plan assets | 7.8 | [1] | ||||||||||||
Quoted Prices in Active Markets for Identical Assets (Level 1)
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Defined Benefit Plan Disclosure [Line Items] | ||||||||||||||
Fair value of plan assets | 218.7 | |||||||||||||
Quoted Prices in Active Markets for Identical Assets (Level 1) | Large-Cap Equity
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Defined Benefit Plan Disclosure [Line Items] | ||||||||||||||
Fair value of plan assets | 94.5 | [1] | ||||||||||||
Quoted Prices in Active Markets for Identical Assets (Level 1) | Small- and Mid-Cap Equity
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Defined Benefit Plan Disclosure [Line Items] | ||||||||||||||
Fair value of plan assets | 19.6 | [1] | ||||||||||||
Quoted Prices in Active Markets for Identical Assets (Level 1) | International Equity
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Defined Benefit Plan Disclosure [Line Items] | ||||||||||||||
Fair value of plan assets | 67.4 | [1],[2] | ||||||||||||
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed Income
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Defined Benefit Plan Disclosure [Line Items] | ||||||||||||||
Fair value of plan assets | 11.2 | [1],[2] | ||||||||||||
Quoted Prices in Active Markets for Identical Assets (Level 1) | Real Assets
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Defined Benefit Plan Disclosure [Line Items] | ||||||||||||||
Fair value of plan assets | 18.2 | [1],[5] | ||||||||||||
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash
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Defined Benefit Plan Disclosure [Line Items] | ||||||||||||||
Fair value of plan assets | 7.8 | [1] | ||||||||||||
Significant Other Observable Inputs (Level 2)
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Defined Benefit Plan Disclosure [Line Items] | ||||||||||||||
Fair value of plan assets | 193.1 | |||||||||||||
Significant Other Observable Inputs (Level 2) | International Equity
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Defined Benefit Plan Disclosure [Line Items] | ||||||||||||||
Fair value of plan assets | 41.9 | [1],[2] | ||||||||||||
Significant Other Observable Inputs (Level 2) | Fixed Income
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Defined Benefit Plan Disclosure [Line Items] | ||||||||||||||
Fair value of plan assets | 151.2 | [1],[2] | ||||||||||||
Significant Unobservable Inputs (Level 3)
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Defined Benefit Plan Disclosure [Line Items] | ||||||||||||||
Fair value of plan assets | 136.2 | |||||||||||||
Significant Unobservable Inputs (Level 3) | Private Equity
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Defined Benefit Plan Disclosure [Line Items] | ||||||||||||||
Fair value of plan assets | 36.0 | [3] | ||||||||||||
Significant Unobservable Inputs (Level 3) | Hedge Funds
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Defined Benefit Plan Disclosure [Line Items] | ||||||||||||||
Fair value of plan assets | 89.1 | [4] | ||||||||||||
Significant Unobservable Inputs (Level 3) | Real Assets
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Defined Benefit Plan Disclosure [Line Items] | ||||||||||||||
Fair value of plan assets | $ 11.1 | [1],[5] | ||||||||||||
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