Principal Payments Due on Long-Term Borrowings (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
2018 (after March 31,)	$ 390.0
2019	450.0
2020	1,000.0
2021	500.0
2022	500.0
Thereafter	2,714.9
Total principal payment	5,554.9	$ 5,580.4
Commercial Paper [Member]
Debt Instrument [Line Items]
2018 (after March 31,)	90.0
Total principal payment	90.0	130.0
2010 Senior Notes [Member]
Debt Instrument [Line Items]
2020	500.0
Total principal payment	500.0	500.0
2012 Senior Notes [Member]
Debt Instrument [Line Items]
2022	500.0
Total principal payment	500.0	500.0
2013 Senior Notes [Member]
Debt Instrument [Line Items]
Thereafter	500.0
Total principal payment	500.0	500.0
2014 Senior Notes (5-Year) [Member]
Debt Instrument [Line Items]
2019	450.0
Total principal payment	450.0	450.0
2014 Senior Notes (30-Year) [Member]
Debt Instrument [Line Items]
Thereafter	600.0
Total principal payment	600.0	600.0
2015 Senior Notes [Member]
Debt Instrument [Line Items]
Thereafter	614.9
Total principal payment	614.9	600.4
2017 Floating Rate Senior Notes [Member]
Debt Instrument [Line Items]
2018 (after March 31,)	300.0
Total principal payment	300.0	300.0
2017 Senior Notes [Member]
Debt Instrument [Line Items]
2021	500.0
Total principal payment	500.0	500.0
2.625% 2017 Notes, due 2023 [Member]
Debt Instrument [Line Items]
Thereafter	500.0
Total principal payment	500.0	500.0
3.25% 2017 Notes, due 2028 [Member]
Debt Instrument [Line Items]
Thereafter	500.0
Total principal payment	500.0	500.0
2017 Term Loan Facility, due 2020 [Member]
Debt Instrument [Line Items]
2020	500.0
Total principal payment	$ 500.0	$ 500.0

Face (par) amount of debt instrument at time of issuance.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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