Tax Charges (Benefits) Recorded Directly to Stockholders' Equity (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Current Tax Benefit (Charge) for Employee Stock Options and Other Stock-Based Plans	$ (7.6)	$ 17.7	$ 8.8
Tax Effect of Other Comprehensive Income	$ 72.4	$ 17.0	$ 18.6

Amount of tax expense (benefit) allocated to other comprehensive income (loss).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=66004124&loc=d3e640-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 20
-Section 45
-Paragraph 11
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65896914&loc=d3e39076-109324

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration