Information Related to Vesting of Performance Based Restricted Stock (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award Performance Options [Line Items]
Tax benefit realized upon exercise	$ 24.3	$ 26.0	$ 43.2
Performance Based Restricted Stock [Member]
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award Performance Options [Line Items]
Fair value of vested shares	23.6	43.1	38.0
Tax benefit realized upon exercise	$ 8.4	$ 15.6	$ 14.4

Schedule of Share based Compensation Arrangements by Share based Payment Award, Performance Options [Line Items]

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- Definition

Disclosure of the aggregate tax benefit realized from the exercise of stock options and the conversion of similar instruments during the annual period.

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

+ Details

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- Definition

Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

+ 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 (d)(2)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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