Stock-Based Compensation - Stock-Based Compensation Expense Recognized (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 6.1	$ 21.7	$ 9.7	$ 33.2
Corporate expenses [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	2.6	4.1	3.3	14.2
Property, general, administrative, and other [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 3.5	$ 17.6	$ 6.4	$ 19.0