Financial Instruments and Risk Management (Details 2) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Fair Value Measurements
Total current derivative contracts, assets	$ 8.2	$ 13.2
Total current derivative contracts, liabilities	29.8	18.4
Total noncurrent derivative contracts, liabilities	20.8	6.3
Discount factor	12-month LIBOR
Fair value of the net receivables related to the European scrap metal program	14.1	16.7
Commodity contracts
Fair Value Measurements
Total current derivative contracts, assets	5.9	10.2
Total noncurrent derivative contracts, assets	0.3	4.2
Total current derivative contracts, liabilities	15.9	9.7
Total noncurrent derivative contracts, liabilities	20.6	5.4
Foreign currency contracts
Fair Value Measurements
Total current derivative contracts, assets	2.3	2.4
Total current derivative contracts, liabilities	12.1	7.7
Total noncurrent derivative contracts, liabilities	0.2	0.4
Other contracts
Fair Value Measurements
Total current derivative contracts, assets		0.6
Interest rate contracts
Fair Value Measurements
Total noncurrent derivative contracts, liabilities		0.5
Interest rate and other contracts
Fair Value Measurements
Total current derivative contracts, liabilities	1.8	1.0
Derivatives Designated As Hedging Instruments
Fair Value Measurements
Total current derivative contracts, assets	3.8	9.3
Total current derivative contracts, liabilities	15.6	12.5
Total noncurrent derivative contracts, liabilities	20.4	6.3
Derivatives Designated As Hedging Instruments | Commodity contracts
Fair Value Measurements
Total current derivative contracts, assets	3.5	9.2
Total noncurrent derivative contracts, assets	0.3	4.2
Total current derivative contracts, liabilities	13.2	9.0
Total noncurrent derivative contracts, liabilities	20.2	5.4
Derivatives Designated As Hedging Instruments | Foreign currency contracts
Fair Value Measurements
Total current derivative contracts, assets	0.3	0.1
Total current derivative contracts, liabilities	1.6	2.5
Total noncurrent derivative contracts, liabilities	0.2	0.4
Derivatives Designated As Hedging Instruments | Interest rate contracts
Fair Value Measurements
Total noncurrent derivative contracts, liabilities		0.5
Derivatives Designated As Hedging Instruments | Interest rate and other contracts
Fair Value Measurements
Total current derivative contracts, liabilities	0.8	1.0
Derivatives Not Designated As Hedging Instruments
Fair Value Measurements
Total current derivative contracts, assets	4.4	3.9
Total current derivative contracts, liabilities	14.2	5.9
Total noncurrent derivative contracts, liabilities	0.4
Derivatives Not Designated As Hedging Instruments | Commodity contracts
Fair Value Measurements
Total current derivative contracts, assets	2.4	1.0
Total current derivative contracts, liabilities	2.7	0.7
Total noncurrent derivative contracts, liabilities	0.4
Derivatives Not Designated As Hedging Instruments | Foreign currency contracts
Fair Value Measurements
Total current derivative contracts, assets	2.0	2.3
Total current derivative contracts, liabilities	10.5	5.2
Derivatives Not Designated As Hedging Instruments | Other contracts
Fair Value Measurements
Total current derivative contracts, assets		0.6
Derivatives Not Designated As Hedging Instruments | Interest rate and other contracts
Fair Value Measurements
Total current derivative contracts, liabilities	$ 1.0