Financial Instruments and Risk Management (Details) (USD $) In Millions, except Share data, unless otherwise specified			9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Commodity contracts item	Sep. 30, 2013 Interest rate swap agreements	Sep. 30, 2013 Currency Exchange Rate Risk	Sep. 30, 2013 Equity contracts	Mar. 31, 2014 Equity contracts
Financial Instruments and Risk Management
Number of methods through which entity manages commodity price risk in connection with market price fluctuations of aluminum ingot			2
Notional amount of derivatives			$ 515	$ 147	$ 723
Notional amount of derivatives which used hedge accounting treatment					93
Period within which derivative will expire			4 years	5 years	2 years
Loss on derivatives included in accumulated other comprehensive earnings (loss), net of tax			(31.3)		(0.6)
Net loss expected to be recognized in the consolidated statement of earnings during the next 12 months			(20.0)		(0.9)
Change in company's stock price (in dollars per share)						$ 1
Impact of change in the company's stock price on pretax earnings						1.4
Notional value of the swap (in shares)						300,000	1,000,000
Combined fair value of the swaps						1.0
Aggregate fair value of derivative instruments with credit-risk-related contingent features that were in a net liability position	42.9	11.0
Collateral amount posted for derivative instruments with credit-risk-related contingent features that were in a net liability position	$ 0	$ 0