Reconciliation of Total Business Segment Assets to Consolidated Assets (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting, Asset Reconciling Item [Line Items]
Cash and cash equivalents	$ 494.3	$ 639.8	$ 655.6	$ 714.9
Deferred income taxes	174.2us-gaap_DeferredTaxAssetsNet	146.9us-gaap_DeferredTaxAssetsNet
Prepaid postretirement assets	19.9us-gaap_PrepaidPensionCosts	83.7us-gaap_PrepaidPensionCosts	3.3us-gaap_PrepaidPensionCosts
Other corporate assets	129.7us-gaap_OtherAssets	119.6us-gaap_OtherAssets	108.1us-gaap_OtherAssets
Assets	2,348.7us-gaap_Assets	2,510.0us-gaap_Assets	2,420.4us-gaap_Assets
Operating Segments
Segment Reporting, Asset Reconciling Item [Line Items]
Deferred income taxes	171.0	136.4	184.3
Assets	$ 1,533.8	$ 1,530.5	$ 1,469.1

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.

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Cumulative employer's contributions in excess of net pension cost recognized, before the adoption of the recognition provisions of FAS 158. Under FAS 158, prepaid pension costs are no longer recognized in the statement of financial position. Note that there is a separate concept for noncurrent assets relating to defined benefit pension and other defined benefit postretirement plans for use under the recognition provisions of FAS 158.

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