Schedule of Restricted Stock Unit and Restricted Stock Activity (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested at beginning of year	0.9	0.8	1.0
Granted, Stock	0.3	0.5	0.5
Vested, Stock	(0.4)	(0.3)	(0.6)
Surrendered, Stock	(0.1)	(0.1)	(0.1)
Non-vested at end of year, Stock	0.7	0.9	0.8
Weighted-Average Grant Price at beginning of year	$ 25.02	$ 23.94	$ 23.33
Granted, Weighted-Average Grant Price	$ 43.33	$ 25.98	$ 24.01
Vested, Weighted-Average Grant Price	$ 24.66	$ 23.93	$ 23.05
Surrendered, Weighted-Average Grant Price	$ 28.88	$ 24.76	$ 24.01
Non-vested at end of year, Weighted-Average Grant Price	$ 32.55	$ 25.02	$ 23.94
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested at beginning of year	5.4	4.3	3.4
Granted, Stock	0.9	1.8	2.0
Vested, Stock	(2.2)	(0.5)	(0.6)
Surrendered, Stock	(0.3)	(0.2)	(0.5)
Non-vested at end of year, Stock	3.8	5.4	4.3

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(iv)(3)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)(iii)(3)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

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

-Publisher FASB

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-Topic 718

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

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-Publisher FASB

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-Topic 718

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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

+ References

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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-Publisher FASB

-Name Accounting Standards Codification

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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-Publisher FASB

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