Income Taxes - Activities Related to Gross Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Balance at beginning of period	$ 15.7	$ 24.2	$ 52.1
Increase in balance related to tax positions taken during current year	0.7	1.0	5.4
Decrease in balance as a result of a lapse of the applicable statues of limitations	(0.9)	(9.5)	(1.3)
Decrease in balance due to settlement with tax authorities	0.0	0.0	(32.1)
Increase in balance related to tax positions taken during prior years	0.3	0.0	0.1
Decrease in balance related to tax positions taken during prior years	(0.2)	0.0	0.0
Balance at end of period	$ 15.6	$ 15.7	$ 24.2

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- Definition

Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Unrecognized Tax Benefit
-URI http://asc.fasb.org/extlink&oid=6527854

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- Definition

Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations.

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