Financial Instruments and Risk Management (Details) € in Millions, item in Millions, $ in Millions, £ in Billions	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Jun. 30, 2015 USD ($)	Jul. 01, 2015 EUR (€)	Jul. 01, 2015 USD ($)	Jun. 30, 2015 EUR (€) item approach	Jun. 30, 2015 GBP (£) item approach	Jun. 30, 2015 USD ($) item approach	Dec. 31, 2014 USD ($)
Financial Instruments and Risk Management
Aggregate fair value of derivative instruments with credit-risk-related contingent features that were in a net liability position								$ 29.8	$ 12.4
Collateral amount posted for derivative instruments with credit-risk-related contingent features that were in a net liability position								$ 0.0	$ 0.0
Commodity 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 | approach						2	2	2
Notional amount of derivatives								$ 295.0
Period within which derivative will expire			3 years
Impact on derivative contracts included in accumulated other comprehensive earnings (loss), net of tax								10.2
Net loss expected to be recognized in the consolidated statement of earnings during the next 12 months			$ 8.8
Commodity contracts | Derivatives Designated As Hedging Instruments | Cash Flow Hedging [Member]
Financial Instruments and Risk Management
Notional amount of derivatives								230.0
Interest rate swap agreements
Financial Instruments and Risk Management
Notional amount of derivatives								146.0
Period within which derivative will expire			4 years
Interest rate swap agreements | Rexam PLC | Income Statement Interest Expense Other
Financial Instruments and Risk Management
Gain included in debt refinancing and other costs			$ 5.0
Interest rate swap agreements | Rexam PLC | Derivatives Not Designated As Hedging Instruments
Financial Instruments and Risk Management
Notional amount of derivatives				€ 300	$ 50.0	€ 1,450		150.0
Period within which derivative will expire			5 years
Interest rate swaption | Rexam PLC | Derivatives Not Designated As Hedging Instruments
Financial Instruments and Risk Management
Notional amount of derivatives | €						€ 750
Currency Exchange Rate Risk
Financial Instruments and Risk Management
Notional amount of derivatives								686.0
Impact on derivative contracts included in accumulated other comprehensive earnings (loss), net of tax								(5.5)
Net loss expected to be recognized in the consolidated statement of earnings during the next 12 months			$ 6.2
Currency Exchange Rate Risk | Rexam PLC
Financial Instruments and Risk Management
Notional amount of derivatives							£ 2.2	$ 3,400.0
Period within which derivative will expire			2 years
Recognized Gains (Losses) of associated with its collar and option contracts	$ 96.0	$ (27.7)
Equity contracts
Financial Instruments and Risk Management
Notional value of the swap (in shares) | item						1	1	1
Fair value of the swaps			$ 2.3