Parent Company Debt Schedule (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014 Rate	Dec. 31, 2013
Debt Instrument
Non-current Portion of Long-term Debt	$ 2,628.7us-gaap_LongTermDebtNoncurrent	$ 2,612.0us-gaap_LongTermDebtNoncurrent
Fair Value Hedge Adjustment, LT Debt
Debt Instrument
Non-current Portion of Long-term Debt	(0.2)	(5.7)
Parent Company
Debt Instrument
Non-current Portion of Long-term Debt	2,230.3	1,875.2
Parent Company \| Fair Value Hedge Adjustment, LT Debt
Debt Instrument
Non-current Portion of Long-term Debt	(0.2)	(5.7)
Notes Issued in 1998 with 2018 Maturity Date \| Senior Notes
Debt Instrument
Debt Instrument, Interest Rate, Stated Percentage	7.00%
Year of Maturity	Dec. 31, 2018
Non-current Portion of Long-term Debt	200.0	200.0
Notes Issued in 1998 with 2018 Maturity Date \| Parent Company \| Senior Notes
Debt Instrument
Debt Instrument, Interest Rate, Stated Percentage	7.00%
Year of Maturity	Dec. 31, 2018
Non-current Portion of Long-term Debt	200.0	200.0
Notes Issued in 1998 with 2028 Maturity Date \| Senior Notes
Debt Instrument
Year of Maturity	Dec. 31, 2028
Non-current Portion of Long-term Debt	365.8	365.8
Notes Issued in 1998 with 2028 Maturity Date \| Parent Company \| Senior Notes
Debt Instrument
Year of Maturity	Dec. 31, 2028
Non-current Portion of Long-term Debt	365.8	365.8
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 \| Minimum \| Parent Company \| 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 1998 with 2028 Maturity Date \| Maximum \| Parent Company \| Senior Notes
Debt Instrument
Debt Instrument, Interest Rate, Stated Percentage	7.25%
Notes Issued in 2002 \| Senior Notes
Debt Instrument
Debt Instrument, Interest Rate, Stated Percentage	7.375%
Year of Maturity	Dec. 31, 2032
Non-current Portion of Long-term Debt	39.5	39.5
Notes Issued in 2002 \| Parent Company \| Senior Notes
Debt Instrument
Debt Instrument, Interest Rate, Stated Percentage	7.375%
Year of Maturity	Dec. 31, 2032
Non-current Portion of Long-term Debt	39.5	39.5
Notes Issued in 2009 \| Senior Notes
Debt Instrument
Debt Instrument, Interest Rate, Stated Percentage	7.125%
Year of Maturity	Dec. 31, 2016
Non-current Portion of Long-term Debt	350.0	350.0
Notes Issued in 2009 \| Parent Company \| Senior Notes
Debt Instrument
Debt Instrument, Interest Rate, Stated Percentage	7.125%
Year of Maturity	Dec. 31, 2016
Non-current Portion of Long-term Debt	350.0	350.0
Notes Issued in 2010 \| Senior Notes
Debt Instrument
Debt Instrument, Interest Rate, Stated Percentage	5.625%
Year of Maturity	Dec. 31, 2020
Non-current Portion of Long-term Debt	399.7	399.7
Notes Issued in 2010 \| Parent Company \| Senior Notes
Debt Instrument
Debt Instrument, Interest Rate, Stated Percentage	5.625%
Year of Maturity	Dec. 31, 2020
Non-current Portion of Long-term Debt	399.7	399.7
Notes Issued in 2012 \| Senior Notes
Debt Instrument
Debt Instrument, Interest Rate, Stated Percentage	5.75%
Year of Maturity	Dec. 31, 2042
Non-current Portion of Long-term Debt	248.7	248.6
Notes Issued in 2012 \| Parent Company \| Senior Notes
Debt Instrument
Debt Instrument, Interest Rate, Stated Percentage	5.75%
Year of Maturity	Dec. 31, 2042
Non-current Portion of Long-term Debt	248.7	248.6
Notes Issued in 2014 \| Senior Notes
Debt Instrument
Debt Instrument, Interest Rate, Stated Percentage	4.00%
Year of Maturity	Dec. 31, 2024
Non-current Portion of Long-term Debt	349.5	0
Notes Issued in 2014 \| Parent Company \| Senior Notes
Debt Instrument
Debt Instrument, Interest Rate, Stated Percentage	4.00%
Year of Maturity	Dec. 31, 2024
Non-current Portion of Long-term Debt	349.5	0
Notes Issued 1990 to 1996 \| Medium-term Notes
Debt Instrument
Debt Instrument, Maturity Date Range, Start	Dec. 31, 2023
Debt Instrument, Maturity Date Range, End	Dec. 31, 2028
Non-current Portion of Long-term Debt	50.8	50.8
Notes Issued 1990 to 1996 \| Parent Company \| Medium-term Notes
Debt Instrument
Debt Instrument, Maturity Date Range, Start	Dec. 31, 2023
Debt Instrument, Maturity Date Range, End	Dec. 31, 2028
Non-current Portion of Long-term Debt	50.8	50.8
Notes Issued 1990 to 1996 \| Minimum \| Medium-term Notes
Debt Instrument
Debt Instrument, Interest Rate, Stated Percentage	7.00%
Notes Issued 1990 to 1996 \| Minimum \| Parent Company \| 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 1990 to 1996 \| Maximum \| Parent Company \| 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
Debt Instrument, Interest Rate, Stated Percentage	7.405%
Year of Maturity	Dec. 31, 2038
Non-current Portion of Long-term Debt	226.5	226.5
Notes Issued in 1998 with 2038 Maturity Date \| Parent Company \| Junior Subordinated Debt
Debt Instrument
Debt Instrument, Interest Rate, Stated Percentage	7.405%
Year of Maturity	Dec. 31, 2038
Non-current Portion of Long-term Debt	$ 226.5	$ 226.5

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

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

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