Summary of Amounts Recognized in Accumulated Other Comprehensive Income Loss (Detail) (Pension Benefits, USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial loss	$ 147.3	$ 135.0
Net prior service cost		0.1
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax	$ 147.3	$ 135.1

The pretax total of net gain (loss), prior service cost (credit), and transition assets (obligations), as well as minimum pension liability if still remaining, included in accumulated other comprehensive income associated with a defined benefit pension or other postretirement plan(s) because they have yet to be recognized as components of net periodic benefit cost.

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The pretax net amount of gains and losses that are not yet recognized as a component of net periodic benefit cost, and that are recognized as increases or decreases in other comprehensive income as they arise. Gains and losses are due to changes in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan.

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- Definition

Amount related to the pretax cost of benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation, which has not yet been recognized as components of net periodic benefit cost.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

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