Retirement Plans - Components of Net Periodic Pension Benefit Cost and Other Changes in Plan Assets and Obligations Recognized in Earnings and Other Comprehensive Earnings (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]
Service cost	$ 0.7us-gaap_DefinedBenefitPlanServiceCost	$ 0.6us-gaap_DefinedBenefitPlanServiceCost	$ 0.4us-gaap_DefinedBenefitPlanServiceCost
Interest cost on benefit obligation	12.7us-gaap_DefinedBenefitPlanInterestCost	11.7us-gaap_DefinedBenefitPlanInterestCost	11.8us-gaap_DefinedBenefitPlanInterestCost
Expected return on plan assets	(18.7)	(17.0)	(15.2)
Amortization of net loss	2.3	7.9	7.2
Settlement	12.0
Net periodic benefit cost (earnings)	9.0	3.2	4.2
Net loss (gain) incurred	42.5	(36.0)	10.6
Settlement recognition	(12.0)
Amortization of net loss	(2.3)	(7.9)	(7.2)
Total recognized in other comprehensive loss (earnings)	28.2	(43.9)	3.4
Total recognized in net periodic pension cost (earnings) and other comprehensive loss (earnings)	37.2	(40.7)	7.6
Amortization of net loss, Estimated	$ 6.0	$ 2.4	$ 7.7

Retirement Plans - Components of Net Periodic Pension Benefit Cost and Other Changes in Plan Assets and Obligations Recognized in Earnings and Other Comprehensive Earnings (Detail) (USD $)
In Millions, unless otherwise specified

12 Months Ended

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]

Service cost

$ 0.7us-gaap_DefinedBenefitPlanServiceCost

$ 0.6us-gaap_DefinedBenefitPlanServiceCost

$ 0.4us-gaap_DefinedBenefitPlanServiceCost

Interest cost on benefit obligation

12.7us-gaap_DefinedBenefitPlanInterestCost

11.7us-gaap_DefinedBenefitPlanInterestCost

11.8us-gaap_DefinedBenefitPlanInterestCost

Expected return on plan assets

(18.7)us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets

(17.0)us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets

(15.2)us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets

Amortization of net loss

2.3us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses

7.9us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses

7.2us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses

Settlement

12.0us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1

Net periodic benefit cost (earnings)

9.0us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost

3.2us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost

4.2us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost

Net loss (gain) incurred

42.5us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax

(36.0)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax

10.6us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax

Settlement recognition

(12.0)us-gaap_DefinedBenefitPlanAmountsRecognizedInOtherComprehensiveIncomeLossNetGainLossBeforeTax

Amortization of net loss

(2.3)us-gaap_OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax

(7.9)us-gaap_OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax

(7.2)us-gaap_OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax

Total recognized in other comprehensive loss (earnings)

28.2us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax

(43.9)us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax

3.4us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax

Total recognized in net periodic pension cost (earnings) and other comprehensive loss (earnings)

37.2us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationBeforeTax

(40.7)us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationBeforeTax

7.6us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationBeforeTax

Amortization of net loss, Estimated

$ 6.0us-gaap_DefinedBenefitPlanAmountToBeAmortizedFromAccumulatedOtherComprehensiveIncomeLossNextFiscalYear

$ 2.4us-gaap_DefinedBenefitPlanAmountToBeAmortizedFromAccumulatedOtherComprehensiveIncomeLossNextFiscalYear

$ 7.7us-gaap_DefinedBenefitPlanAmountToBeAmortizedFromAccumulatedOtherComprehensiveIncomeLossNextFiscalYear

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The amount of gains or losses recognized in net periodic benefit cost.

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Amount before tax, after reclassification adjustments, of actuarial gain (loss) that has not been recognized in the income statement.

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Amount included in accumulated other comprehensive income (AOCI) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position, including gain (loss), prior service cost (credit), and transition asset (obligation).

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An amount calculated as a basis for determining the extent of delayed recognition of the effects of changes in the fair value of assets. The expected return on plan assets is determined based on the expected long-term rate of return on plan assets and the market-related value of plan assets.

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The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.

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The total amount of net periodic benefit cost for defined benefit plans for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments.

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Amount of net gain (loss) recognized in net periodic benefit cost as a result of an irrevocable action that relieves the employer (or the plan) of primary responsibility for a benefit obligation and eliminates significant risks related to the obligation and the assets used to effect the settlement. Examples of transactions that constitute a settlement include, but are not limited to, lump-sum cash payments to plan participants in exchange for their rights to receive specified benefits and purchasing nonparticipating annuity contracts to cover vested benefits.

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The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.

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Amount before tax of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) related to pension and other postretirement benefit plans.

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Amount before tax of (increase) decrease in the value of the projected benefit obligation related to a change in an actuarial assumption and increase (decrease) in the value of the plan assets resulting from experience different from that assumed, that has not been recognized in net periodic benefit (cost) credit.

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Amount before tax of reclassification adjustment from accumulated other comprehensive income (loss) for actuarial gain (loss) related to pension and other postretirement benefit plans.

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Amount before tax of reclassification adjustment from accumulated other comprehensive income (loss) for net transition asset (obligation) related to pension and other postretirement benefit plans.

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