Financial Instruments - Additional Information (Detail) $ in Millions	3 Months Ended
Jun. 30, 2021 USD ($) Customer	Jun. 30, 2020 Customer	Dec. 31, 2020 USD ($)
Debt Instrument [Line Items]
Long-term debt, carrying values	$ 2,867.3		$ 2,625.8
Long-term debt, fair values	$ 3,220.0		$ 3,080.0
Customer Concentration Risk \| Total Revenues
Debt Instrument [Line Items]
Number of customer accounted for 10% or more of consolidated total revenues \| Customer	0	0
Customer Concentration Risk \| Total Revenues \| Minimum
Debt Instrument [Line Items]
Percentage of concentration risk	10.00%	10.00%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
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-URI http://asc.fasb.org/extlink&oid=121572278&loc=d3e13531-108611

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592

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