New Accounting Pronouncements - Narrative (Detail) - Accounting Standards Update 2017-07 - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
New accounting pronouncement effect on operating results	$ (4.2)	$ (8.3)
Other Non-operating Income [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Effect on other non-operating income from the adoption of a new accounting pronouncement	$ 4.2	$ 8.3

Amount of the effect of a change in accounting principle on operating profit or loss.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=64853466&loc=d3e22499-107794

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64853466&loc=d3e22580-107794

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64853466&loc=d3e22583-107794

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