Income Taxes - Tabular Reconciliation of Total Amounts of Unrecognized Tax Benefits (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Balance at January 1	$ 304.3us-gaap_UnrecognizedTaxBenefits	$ 285.5us-gaap_UnrecognizedTaxBenefits	$ 158.4us-gaap_UnrecognizedTaxBenefits
Increases related to prior periods	0.9	16.5	118.7
Decreases related to prior periods	(3.8)	(17.3)	(8.9)
Increases related to current period	17.3	22.5	19.1
Decreases related to settlements with taxing authorities	(3.0)	(2.9)	(0.6)
Decreases related to lapse of statute of limitations	(1.7)		(1.2)
Balance at December 31	314.0us-gaap_UnrecognizedTaxBenefits	304.3us-gaap_UnrecognizedTaxBenefits	285.5us-gaap_UnrecognizedTaxBenefits
Amounts impacting effective tax rate, if recognized balance at December 31	$ 203.0	$ 186.3	$ 159.0

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

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Unrecognized Tax Benefit

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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 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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