Debt Schedule (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Debt Instrument
Non-current Portion of Long-term Debt	$ 2,628.7us-gaap_LongTermDebtNoncurrent	$ 2,612.0us-gaap_LongTermDebtNoncurrent
Long-term Debt, Current Maturities	151.9us-gaap_LongTermDebtCurrent	0us-gaap_LongTermDebtCurrent
Long-term Debt	2,780.6us-gaap_LongTermDebt	2,612.0us-gaap_LongTermDebt
Fair Value Hedge Adjustment, LT Debt
Debt Instrument
Non-current Portion of Long-term Debt	(0.2)	(5.7)
Secured Notes Issued in 2007 \| Senior Notes
Debt Instrument
Non-current Portion of Long-term Debt	398.4	440.0
Year of Maturity	Dec. 31, 2037
Interest Rate Terms	Variable
Notes Issued in 1998 with 2018 Maturity Date \| Senior Notes
Debt Instrument
Non-current Portion of Long-term Debt	200.0	200.0
Year of Maturity	Dec. 31, 2018
Debt Instrument, Interest Rate, Stated Percentage	7.00%
Notes Issued in 1998 with 2028 Maturity Date \| Senior Notes
Debt Instrument
Non-current Portion of Long-term Debt	365.8	365.8
Year of Maturity	Dec. 31, 2028
Notes Issued in 1998 with 2028 Maturity Date \| Minimum \| Senior Notes
Debt Instrument
Debt Instrument, Interest Rate, Stated Percentage	6.75%
Notes Issued in 1998 with 2028 Maturity Date \| Maximum \| Senior Notes
Debt Instrument
Debt Instrument, Interest Rate, Stated Percentage	7.25%
Notes Issued in 2002 \| Senior Notes
Debt Instrument
Non-current Portion of Long-term Debt	39.5	39.5
Year of Maturity	Dec. 31, 2032
Debt Instrument, Interest Rate, Stated Percentage	7.375%
Notes Issued in 2005
Debt Instrument
Long-term Debt, Current Maturities	151.9	0
Year of Maturity	Dec. 31, 2015
Debt Instrument, Interest Rate, Stated Percentage	6.85%
Notes Issued in 2005 \| Senior Notes
Debt Instrument
Non-current Portion of Long-term Debt	0	296.8
Year of Maturity	Dec. 31, 2015
Debt Instrument, Interest Rate, Stated Percentage	6.85%
Notes Issued in 2009 \| Senior Notes
Debt Instrument
Non-current Portion of Long-term Debt	350.0	350.0
Year of Maturity	Dec. 31, 2016
Debt Instrument, Interest Rate, Stated Percentage	7.125%
Notes Issued in 2010 \| Senior Notes
Debt Instrument
Non-current Portion of Long-term Debt	399.7	399.7
Year of Maturity	Dec. 31, 2020
Debt Instrument, Interest Rate, Stated Percentage	5.625%
Notes Issued in 2012 \| Senior Notes
Debt Instrument
Non-current Portion of Long-term Debt	248.7	248.6
Year of Maturity	Dec. 31, 2042
Debt Instrument, Interest Rate, Stated Percentage	5.75%
Notes Issued in 2014 \| Senior Notes
Debt Instrument
Non-current Portion of Long-term Debt	349.5	0
Year of Maturity	Dec. 31, 2024
Debt Instrument, Interest Rate, Stated Percentage	4.00%
Notes Issued 1990 to 1996 \| Medium-term Notes
Debt Instrument
Non-current Portion of Long-term Debt	50.8	50.8
Debt Instrument, Maturity Date Range, Start	Dec. 31, 2023
Debt Instrument, Maturity Date Range, End	Dec. 31, 2028
Notes Issued 1990 to 1996 \| Minimum \| Medium-term Notes
Debt Instrument
Debt Instrument, Interest Rate, Stated Percentage	7.00%
Notes Issued 1990 to 1996 \| Maximum \| Medium-term Notes
Debt Instrument
Debt Instrument, Interest Rate, Stated Percentage	7.19%
Notes Issued in 1998 with 2038 Maturity Date \| Junior Subordinated Debt
Debt Instrument
Non-current Portion of Long-term Debt	$ 226.5	$ 226.5
Year of Maturity	Dec. 31, 2038
Debt Instrument, Interest Rate, Stated Percentage	7.405%

Contractual interest rate for funds borrowed, under the debt agreement.

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Description of the interest rate as being fixed or variable, and, if variable, identification of the index or rate on which the interest rate is based and the number of points or percentage added to that index or rate to set the rate, and other pertinent information, such as frequency of rate resets.

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Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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Latest date the outstanding debt instruments are required to be repaid, in CCYY-MM-DD format.

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Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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