Other Financial Statement Data (Details) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Other current assets    
Final price deferred $ 112.8 [1] $ 49.9 [1]
Income and other taxes receivable 151.7 201.9
Prepaid expenses 75.2 63.8
Other 51.7 52.6
Total other current assets 391.4 368.2
Accrued liabilities    
Non-income taxes 40.9 29.9
Payroll and employee benefits 114.1 172.8
Asset retirement obligations 115.9 87.9
Customer prepayments 219.4 101.6
Other 363.1 333.9
Total accrued liabilities, current 853.4 726.1
Other noncurrent liabilities    
Asset retirement obligations 729.2 771.6
Accrued pension and postretirement benefits 71.2 77.6
Unrecognized tax benefits 66.1 89.2
Other 261.6 261.6
Total other noncurrent liabilities $ 1,128.1 $ 1,200.0
[1] Final price deferred is product that has shipped to customers, but the price has not yet been agreed upon. This has not been included in inventory as risk of loss has passed to our customers. Amounts in this account are based on inventory cost.