Senior Notes and Long-Term Debt - Senior Notes (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Senior Notes	$ 2,011.3	$ 1,497.3
Fixed Rate Due Nov. 2020
Debt Instrument [Line Items]
Interest Rate	3.45%
Senior Notes	$ 499.7	499.6
Fixed Rate Due Aug. 2021
Debt Instrument [Line Items]
Interest Rate	3.38%
Senior Notes	$ 499.1	498.8
Fixed Rate Due Aug. 2022
Debt Instrument [Line Items]
Interest Rate	2.38%
Senior Notes	$ 499.2	498.9
Fixed Rate Due Aug. 2028
Debt Instrument [Line Items]
Interest Rate	3.65%
Senior Notes	$ 513.3	$ 0.0

Contractual interest rate for funds borrowed, under the debt agreement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16(a))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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-Name Accounting Standards Codification
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-Section S99
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