Financial Instruments and Risk Management (Details) (USD $) In Millions, except Share data, unless otherwise specified			6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2014 Commodity contracts item	Jun. 30, 2014 Interest rate swap agreements	Jun. 30, 2014 Currency Exchange Rate Risk	Jun. 30, 2014 Equity contracts	Mar. 31, 2015 Equity contracts	Sep. 30, 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			$ 443	$ 105	$ 810
Period within which derivative will expire			4 years	4 years	2 years
Loss on derivatives included in accumulated other comprehensive earnings (loss), net of tax			19.9		2.4
Net loss expected to be recognized in the consolidated statement of earnings during the next 12 months			10.7		3.1
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)							1,000,000	300,000
Combined fair value of the swaps						1.8
Aggregate fair value of derivative instruments with credit-risk-related contingent features that were in a net liability position	25.4	48.0
Collateral amount posted for derivative instruments with credit-risk-related contingent features that were in a net liability position	$ 0	$ 0