Investments - Investments in Short and Long-Term Classified as Available-for-Sale Securities (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	$ 869.3	$ 807.3
Available-for-sale Securities, Gross Unrealized Gains	0.1	0.5
Available-for-sale Securities, Gross Unrealized Losses	(0.5)	(0.1)
Available-for-sale Securities, Fair Value	868.9	807.7
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	516.9	457.6
Available-for-sale Securities, Gross Unrealized Gains	0.1	0.4
Available-for-sale Securities, Gross Unrealized Losses	(0.5)	(0.1)
Available-for-sale Securities, Fair Value	516.5	457.9
U.S. Government and Agency Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	194.3	211.1
Available-for-sale Securities, Gross Unrealized Gains		0.1
Available-for-sale Securities, Fair Value	194.3	211.2
Foreign Government Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		3.1
Available-for-sale Securities, Fair Value		3.1
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	57.8	68.3
Available-for-sale Securities, Fair Value	57.8	68.3
Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	100.3	67.2
Available-for-sale Securities, Fair Value	$ 100.3	$ 67.2

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 10

-Section 50

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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Amount of debt securities categorized neither as held-to-maturity nor trading.

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