Parent Company Debt Schedule (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument
Non-current Portion of Long-term Debt		$ 2,475.1		$ 2,628.7
Current Maturities of Long-term Debt		352.4		151.9
Long-term Debt		2,827.5		2,780.6
Fair Value Hedge Adjustment, LT Debt
Debt Instrument
Non-current Portion of Long-term Debt		(2.7)		(0.2)
Current Maturities of Long-term Debt		2.4		0.0
Parent Company
Debt Instrument
Non-current Portion of Long-term Debt		2,151.1		2,230.3
Current Maturities of Long-term Debt		352.4		0.0
Long-term Debt		2,503.5		2,230.3
Parent Company | Fair Value Hedge Adjustment, LT Debt
Debt Instrument
Non-current Portion of Long-term Debt		(2.7)		(0.2)
Current Maturities of Long-term Debt		2.4		0.0
Notes Issued in 1998 with 2018 Maturity Date | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			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
Stated Interest Rate of Debt			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
Stated Interest Rate of Debt			6.75%
Notes Issued in 1998 with 2028 Maturity Date | Minimum | Parent Company | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			6.75%
Notes Issued in 1998 with 2028 Maturity Date | Maximum | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			7.25%
Notes Issued in 1998 with 2028 Maturity Date | Maximum | Parent Company | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			7.25%
Notes Issued in 2002 | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			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
Stated Interest Rate of Debt			7.375%
Year of Maturity	Dec. 31, 2032
Non-current Portion of Long-term Debt		39.5		39.5
Notes Issued in 2009
Debt Instrument
Stated Interest Rate of Debt			7.125%
Year of Maturity	Dec. 31, 2016
Current Maturities of Long-term Debt		350.0		0.0
Notes Issued in 2009 | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			7.125%
Year of Maturity	Dec. 31, 2016
Non-current Portion of Long-term Debt		0.0		350.0
Notes Issued in 2009 | Parent Company
Debt Instrument
Stated Interest Rate of Debt			7.125%
Year of Maturity	Dec. 31, 2016
Current Maturities of Long-term Debt		350.0		0.0
Notes Issued in 2009 | Parent Company | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			7.125%
Year of Maturity	Dec. 31, 2016
Non-current Portion of Long-term Debt		0.0		350.0
Notes Issued in 2010 | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			5.625%
Year of Maturity	Dec. 31, 2020
Non-current Portion of Long-term Debt		399.8		399.7
Notes Issued in 2010 | Parent Company | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			5.625%
Year of Maturity	Dec. 31, 2020
Non-current Portion of Long-term Debt		399.8		399.7
Notes Issued in 2012 | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			5.75%
Year of Maturity	Dec. 31, 2042
Non-current Portion of Long-term Debt		248.7		248.7
Notes Issued in 2012 | Parent Company | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			5.75%
Year of Maturity	Dec. 31, 2042
Non-current Portion of Long-term Debt		248.7		248.7
Notes Issued in 2014 | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			4.00%
Year of Maturity	Dec. 31, 2024
Non-current Portion of Long-term Debt		349.5		349.5
Notes Issued in 2014 | Parent Company | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			4.00%
Year of Maturity	Dec. 31, 2024
Non-current Portion of Long-term Debt		349.5		349.5
Notes Issued in 2015 | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			3.875%
Year of Maturity	Dec. 31, 2025
Non-current Portion of Long-term Debt		273.2		0.0
Notes Issued in 2015 | Parent Company | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			3.875%
Year of Maturity	Dec. 31, 2025
Non-current Portion of Long-term Debt		273.2		0.0
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
Stated Interest Rate of Debt			7.00%
Notes Issued 1990 to 1996 | Minimum | Parent Company | Medium-term Notes
Debt Instrument
Stated Interest Rate of Debt			7.00%
Notes Issued 1990 to 1996 | Maximum | Medium-term Notes
Debt Instrument
Stated Interest Rate of Debt			7.19%
Notes Issued 1990 to 1996 | Maximum | Parent Company | Medium-term Notes
Debt Instrument
Stated Interest Rate of Debt			7.19%
Notes Issued in 1998 with 2038 Maturity Date | Junior Subordinated Debt
Debt Instrument
Stated Interest Rate of Debt	7.405%		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
Stated Interest Rate of Debt	7.405%		7.405%
Year of Maturity	Dec. 31, 2038
Non-current Portion of Long-term Debt		$ 226.5		$ 226.5