Principal Payments Due on Long-Term Borrowings (Detail) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
2017 (after June 30,)
2018	300.0
2019	450.0
2020	500.0
2021	500.0
Thereafter	3,170.3
Total principal amount	4,920.3	$ 3,377.4
2010 Senior Notes [Member]
Debt Instrument [Line Items]
2020	500.0
Total principal amount	500.0	500.0
2012 Senior Notes [Member]
Debt Instrument [Line Items]
Thereafter	500.0
Total principal amount	500.0	500.0
2013 Senior Notes [Member]
Debt Instrument [Line Items]
Thereafter	500.0
Total principal amount	500.0	500.0
2014 Senior Notes (5-Year) [Member]
Debt Instrument [Line Items]
2019	450.0
Total principal amount	450.0	450.0
2014 Senior Notes (30-Year) [Member]
Debt Instrument [Line Items]
Thereafter	600.0
Total principal amount	600.0	600.0
2015 Senior Notes [Member]
Debt Instrument [Line Items]
Thereafter	570.3
Total principal amount	570.3	$ 527.4
2017 Floating Rate Senior Notes [Member]
Debt Instrument [Line Items]
2018	300.0
Total principal amount	300.0
2017 Senior Notes [Member]
Debt Instrument [Line Items]
2021	500.0
Total principal amount	500.0
2.65% 2017 Private Placement Notes, due 2023 [Member]
Debt Instrument [Line Items]
Thereafter	500.0
Total principal amount	500.0
3.25% 2017 Private Placement Notes, due 2028 [Member]
Debt Instrument [Line Items]
Thereafter	500.0
Total principal amount	$ 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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

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