Fair Value and Carrying Value of Long-Term Debt (Detail) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Long Term Debt Noncurrent	$ 3,106.1	$ 2,547.3
Estimated Fair Value	3,237.2	2,772.7
Series 2007-1 Notes [Member]
Debt Instrument [Line Items]
Notes Payable	300.0	300.0
Estimated Fair Value	328.6	334.6
2010 Senior Notes [Member]
Debt Instrument [Line Items]
Notes Payable	504.7	503.8
Estimated Fair Value	559.4	564.4
2012 Senior Notes [Member]
Debt Instrument [Line Items]
Notes Payable	497.0	496.9
Estimated Fair Value	531.1	537.1
2013 Senior Notes [Member]
Debt Instrument [Line Items]
Notes Payable	497.6	497.5
Estimated Fair Value	535.5	548.4
2014 Senior Notes (5-Year) [Member]
Debt Instrument [Line Items]
Notes Payable	451.3	450.7
Estimated Fair Value	454.6	454.3
2014 Senior Notes (30-Year) [Member]
Debt Instrument [Line Items]
Notes Payable	298.4	298.4
Estimated Fair Value	309.1	333.9
2015 Senior Notes [Member]
Debt Instrument [Line Items]
Notes Payable	557.1	0.0
Estimated Fair Value	$ 518.9	$ 0.0

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13433-108611

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Carrying amount of long-term debt, net of unamortized discount or premium, excluding amounts to be repaid within one year or the normal operating cycle, if longer (current maturities). Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22)

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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-Name Regulation S-X (SX)

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Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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-Subparagraph (SX 210.7-03.16(a))

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

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-Section S99

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-Name Regulation S-X (SX)

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