Long-Term Debt - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended				9 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Covenant Requirement Minimum	Sep. 30, 2012 Covenant Requirement Maximum	Sep. 30, 2012 Senior Unsecured Notes 5.25 Percent Due 2022	Mar. 13, 2012 Senior Unsecured Notes 5.25 Percent Due 2022	Sep. 30, 2012 Senior Unsecured Notes 4.9 percent	Jul. 12, 2012 Senior Unsecured Notes 4.9 percent	Sep. 30, 2012 Senior Unsecured Notes 8.5 Percent Due 2018	Sep. 30, 2012 Senior Unsecured Notes 8.5 Percent Due 2018	Sep. 30, 2012 Senior Unsecured Notes 5.25 Percent	Sep. 30, 2012 Senior Unsecured Notes 6.875 Percent Due 2020
Debt Instrument [Line Items]
Senior notes, aggregate principal amount							$ 500.0		$ 800.0			$ 1,300.0	$ 650.0
Debt, interest rate						5.25%		4.90%		8.50%		5.25%	6.875%
Debt, due date						2022				2018	2018		2020
Principal payments on long-term debt		600.4	0.5							600.0
Loss on extinguishment of debt	(82.1)	(82.1)									82.1
Senior notes, net of original issue discount or premiums												1,315.4	645.0
Revolving credit facility	950.0	950.0
Revolving credit facility, interest rate, additional to LIBOR		1.75%
Revolving credit facility, interest rate, additional to Prime		0.75%
Revolving credit facility agreement		Borrowings under the Revolving Credit Facility bear interest at an annual rate equal to the London interbank offered rate ("LIBOR") (as defined in the Revolving Credit Facility) plus 175 basis points or Prime (as defined in the Revolving Credit Facility) plus 75 basis points.
Revolving credit facility, average interest rate	2.10%	2.10%
Outstanding letter of credit amount	$ 9.0	$ 9.0
Interest coverage ratio				2.0
Total leverage ratio					4.25