Investment in Affiliates and Other Assets - Components of Net Capitalized Permit Costs (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Other Noncurrent Assets [Line Items]
Net capitalized permit costs	$ 59.5	$ 65.7
Pending Renewals Of Prior Permits
Other Noncurrent Assets [Line Items]
Net capitalized permit costs		0.2
LLRW License - (expires in 2024) | Permits Subject to Amortization
Other Noncurrent Assets [Line Items]
Net capitalized permit costs	54.0	58.3
Byproduct License - (expires in 2018) | Permits Subject to Amortization
Other Noncurrent Assets [Line Items]
Net capitalized permit costs	4.6	5.6
Other - (expires 2014 - 2024) | Permits Subject to Amortization
Other Noncurrent Assets [Line Items]
Net capitalized permit costs	$ 0.9	$ 1.6