Income Taxes - Tabular Reconciliation of Total Amounts of 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 January 1	$ 321.7	$ 311.0	$ 293.9
Increase related to the merger	247.6
Increases related to prior periods	1.3	0.9	16.5
Decreases related to prior periods		(3.8)	(17.3)
Increases related to current period	25.7	18.3	20.8
Decreases related to settlements with taxing authorities	(1.4)	(3.0)	(2.9)
Decreases related to lapse of statute of limitations	(3.0)	(1.7)
Balance at December 31	591.9	321.7	311.0
Amounts impacting effective tax rate, if recognized balance at December 31	$ 526.6	$ 186.3	$ 191.2

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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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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 acquisitions.

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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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The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

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