Principal Payments Due on Long-Term Borrowings (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Total principal payment	$ 5,580.4	$ 3,377.4
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	600.4
Total principal payment	600.4	$ 527.4
2017 Floating Rate Senior Notes [Member]
Debt Instrument [Line Items]
2018	300.0
Total principal payment	300.0
2017 Term Loan Facility, due 2020 [Member]
Debt Instrument [Line Items]
2020	500.0
Total principal payment	500.0
2017 Senior Notes [Member]
Debt Instrument [Line Items]
2021	500.0
Total principal payment	500.0
2.625% 2017 Private Placement Notes, due 2023 [Member]
Debt Instrument [Line Items]
Thereafter	500.0
Total principal payment	500.0
3.25% 2017 Private Placement Notes, due 2028 [Member]
Debt Instrument [Line Items]
Thereafter	500.0
Total principal payment	500.0
Commercial Paper [Member]
Debt Instrument [Line Items]
2018	130.0
Total principal payment	$ 130.0

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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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