Fair Value Measurements, Fair Value Hierarchy Table (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Financial Assets:
Investment Percentage in Industrial Sector	61.00%		53.00%
Investment Percentage in Financial Sector	33.00%		38.00%
Investment Percentage in Utilities Sector	6.00%		9.00%
Level 2 to Level 1 transfers			$ 220.7
Recurring
Financial Assets:
Cash and cash equivalents	273.4	[1]	49.8	[1]
Available for sale securities	5.6		4.9
Total Assets	1,152.9		677.3
Financial Liabilities:
Convertible Notes	(240.1)		(203.0)
Total Liabilities	556.8		278.2
Recurring | Fixed income investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	427.7	[2]	413.3	[2]
Recurring | Mortgage backed securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	31.5		33.9
Recurring | Corporate debt securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	40.4	[3]	39.1	[3]
Recurring | Equity investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	172.9	[4]	52.3	[4]
Recurring | United States Treasuries
Financial Assets:
VEBAs and Canadian Pension Plan Assets	13.6		1.6
Recurring | Municipal debt securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	3.9		6.3
Recurring | Cash and money market investments
Financial Assets:
VEBAs and Canadian Pension Plan Assets	16.4	[5]	12.1	[5]
Recurring | Asset backed securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	3.2		5.0
Recurring | Diversified investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	12.1	[6]	12.3	[6]
Recurring | Equity Securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	8.7
Recurring | Aluminum | Fixed priced purchase contracts
Financial Assets:
Derivative Assets	2.6		0.3
Financial Liabilities:
Derivative Liabilities	(0.5)		(7.8)
Recurring | Aluminum | Midwest premium swap contracts
Financial Assets:
Derivative Assets	0.4		0.1
Financial Liabilities:
Derivative Liabilities			(0.1)
Recurring | Natural Gas | Fixed priced purchase contracts
Financial Assets:
Derivative Assets	0.2
Financial Liabilities:
Derivative Liabilities	(2.6)		(1.3)
Recurring | Natural Gas | Put option sales contracts
Financial Liabilities:
Derivative Liabilities	(0.5)		(5.6)
Recurring | Electricity | Fixed priced purchase contracts
Financial Liabilities:
Derivative Liabilities	(1.0)		(1.8)
Recurring | Hedges Relating to the Convertible Notes | Call Options
Financial Assets:
Derivative Assets	55.3		46.3
Recurring | Hedges Relating to the Convertible Notes | Bifurcated Conversion Feature
Financial Liabilities:
Derivative Liabilities	(62.1)		(53.9)
Recurring | Level 1
Financial Assets:
Cash and cash equivalents	107.9	[1]	49.8	[1]
Available for sale securities	0		0
Total Assets	445.8		282.6
Financial Liabilities:
Convertible Notes	(240.1)		(203.0)
Total Liabilities	490.1		203.0
Recurring | Level 1 | Fixed income investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	192.3	[2]	183.5	[2],[7]
Recurring | Level 1 | Mortgage backed securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 1 | Corporate debt securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 1 | Equity investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	114.1		29.8	[4],[7]
Recurring | Level 1 | United States Treasuries
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 1 | Municipal debt securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 1 | Cash and money market investments
Financial Assets:
VEBAs and Canadian Pension Plan Assets	16.4	[5]	12.1	[5]
Recurring | Level 1 | Asset backed securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 1 | Diversified investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	6.4	[6]	7.4	[6],[7]
Recurring | Level 1 | Equity Securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	8.7
Recurring | Level 1 | Aluminum | Fixed priced purchase contracts
Financial Assets:
Derivative Assets	0		0
Financial Liabilities:
Derivative Liabilities	0		0
Recurring | Level 1 | Aluminum | Midwest premium swap contracts
Financial Assets:
Derivative Assets	0		0
Financial Liabilities:
Derivative Liabilities			0
Recurring | Level 1 | Natural Gas | Fixed priced purchase contracts
Financial Assets:
Derivative Assets	0
Financial Liabilities:
Derivative Liabilities	0		0
Recurring | Level 1 | Natural Gas | Put option sales contracts
Financial Liabilities:
Derivative Liabilities	0		0
Recurring | Level 1 | Electricity | Fixed priced purchase contracts
Financial Liabilities:
Derivative Liabilities	0		0
Recurring | Level 1 | Hedges Relating to the Convertible Notes | Call Options
Financial Assets:
Derivative Assets	0		0
Recurring | Level 1 | Hedges Relating to the Convertible Notes | Bifurcated Conversion Feature
Financial Liabilities:
Derivative Liabilities	0		0
Recurring | Level 2
Financial Assets:
Cash and cash equivalents	165.5	[1]	0
Available for sale securities	5.6		4.9
Total Assets	706.7		394.6
Financial Liabilities:
Convertible Notes	0		0
Total Liabilities	66.7		75.1
Recurring | Level 2 | Fixed income investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	235.4	[2]	229.8	[2],[7]
Recurring | Level 2 | Mortgage backed securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	31.5		33.9
Recurring | Level 2 | Corporate debt securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	40.4	[3]	39.1	[3]
Recurring | Level 2 | Equity investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	58.8	[4]	22.5	[4],[7]
Recurring | Level 2 | United States Treasuries
Financial Assets:
VEBAs and Canadian Pension Plan Assets	13.6		1.6
Recurring | Level 2 | Municipal debt securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	3.9		6.3
Recurring | Level 2 | Cash and money market investments
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 2 | Asset backed securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	3.2		5.0
Recurring | Level 2 | Diversified investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	5.7	[6]	4.9	[6],[7]
Recurring | Level 2 | Equity Securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0
Recurring | Level 2 | Aluminum | Fixed priced purchase contracts
Financial Assets:
Derivative Assets	2.6		0.3
Financial Liabilities:
Derivative Liabilities	(0.5)		(7.8)
Recurring | Level 2 | Aluminum | Midwest premium swap contracts
Financial Assets:
Derivative Assets	0		0
Financial Liabilities:
Derivative Liabilities			0
Recurring | Level 2 | Natural Gas | Fixed priced purchase contracts
Financial Assets:
Derivative Assets	0.2
Financial Liabilities:
Derivative Liabilities	(2.6)		(1.3)
Recurring | Level 2 | Natural Gas | Put option sales contracts
Financial Liabilities:
Derivative Liabilities	(0.5)		(5.6)
Recurring | Level 2 | Electricity | Fixed priced purchase contracts
Financial Liabilities:
Derivative Liabilities	(1.0)		(1.8)
Recurring | Level 2 | Hedges Relating to the Convertible Notes | Call Options
Financial Assets:
Derivative Assets	55.3		46.3
Recurring | Level 2 | Hedges Relating to the Convertible Notes | Bifurcated Conversion Feature
Financial Liabilities:
Derivative Liabilities	(62.1)		(53.9)
Recurring | Level 3
Financial Assets:
Cash and cash equivalents	0		0
Available for sale securities	0		0
Total Assets	0.4		0.1
Financial Liabilities:
Convertible Notes	0		0
Total Liabilities	0		0.1
Recurring | Level 3 | Fixed income investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 3 | Mortgage backed securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 3 | Corporate debt securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 3 | Equity investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 3 | United States Treasuries
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 3 | Municipal debt securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 3 | Cash and money market investments
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 3 | Asset backed securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 3 | Diversified investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 3 | Equity Securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0
Recurring | Level 3 | Aluminum | Fixed priced purchase contracts
Financial Assets:
Derivative Assets	0		0
Financial Liabilities:
Derivative Liabilities	0		0
Recurring | Level 3 | Aluminum | Midwest premium swap contracts
Financial Assets:
Derivative Assets	0.4		0.1
Financial Liabilities:
Derivative Liabilities			(0.1)
Recurring | Level 3 | Natural Gas | Fixed priced purchase contracts
Financial Assets:
Derivative Assets	0
Financial Liabilities:
Derivative Liabilities	0		0
Recurring | Level 3 | Natural Gas | Put option sales contracts
Financial Liabilities:
Derivative Liabilities	0		0
Recurring | Level 3 | Electricity | Fixed priced purchase contracts
Financial Liabilities:
Derivative Liabilities	0		0
Recurring | Level 3 | Hedges Relating to the Convertible Notes | Call Options
Financial Assets:
Derivative Assets	0		0
Recurring | Level 3 | Hedges Relating to the Convertible Notes | Bifurcated Conversion Feature
Financial Liabilities:
Derivative Liabilities	0		0
Nichols Promissory Note | Recurring
Financial Liabilities:
Promissory Note			(4.7)
Nichols Promissory Note | Recurring | Level 1
Financial Liabilities:
Promissory Note			0
Nichols Promissory Note | Recurring | Level 2
Financial Liabilities:
Promissory Note			(4.7)
Nichols Promissory Note | Recurring | Level 3
Financial Liabilities:
Promissory Note			0
Senior Notes | Recurring
Financial Liabilities:
Senior Notes	(250.0)
Senior Notes | Recurring | Level 1
Financial Liabilities:
Senior Notes	(250.0)
Senior Notes | Recurring | Level 2
Financial Liabilities:
Senior Notes	0
Senior Notes | Recurring | Level 3
Financial Liabilities:
Senior Notes	0
Commercial paper, not included with Cash and Cash Equivalents | Recurring
Financial Assets:
Short-term investments	85.0
Commercial paper, not included with Cash and Cash Equivalents | Recurring | Level 1
Financial Assets:
Short-term investments	0
Commercial paper, not included with Cash and Cash Equivalents | Recurring | Level 2
Financial Assets:
Short-term investments	85.0
Commercial paper, not included with Cash and Cash Equivalents | Recurring | Level 3
Financial Assets:
Short-term investments	0

[1] See Note 2 for components of cash and cash equivalents.

[2] This category represents investments in various fixed income funds with multiple registered investment companies. Such funds invest in diversified portfolios, including (a) marketable fixed income securities such as (i) U.S. Treasury and other government and agency securities, (ii) municipal bonds, (iii) mortgage-backed securities, (iv) asset-backed securities, (v) corporate bonds, notes and debentures in various sectors, (vi) preferred and common stock, (vii) investments in affiliated and other investment companies, (viii) short-term investments and other net assets and (vii) repurchase agreements and reverse repurchase agreements, (b) other commingled investments, (c) investment grade debt, and (d) fixed income instruments which may be represented by options, future contracts or swap agreements. The fair value of assets in this category is estimated using the net asset value per share of the investments.

[3] This category represents investments in fixed income corporate securities in various sectors. Investments in the industrial, financial and utilities sectors in 2012 represented approximately 61%, 33% and 6% of the total portfolio in this category, respectively. Investments in the industrial, financial and utilities sectors in 2011 represented approximately 53%, 38% and 9% of the total portfolio in this category, respectively. The fair value of assets in this category is estimated using the net asset value per share of the investments.

[4] This category represents investments in equity funds that invest in portfolios comprised of (i) equity securities of U.S. companies across all market capitalization, (ii) American Depositary Receipts, or ADRs, for securities of non-U.S. issuers, (iii) securities whose principal market is outside of U.S, and (iv) other short term investments. The fair value of assets in this category is determined by using quoted prices in active markets for investments considered Level 1 inputs and estimated using the net asset value per share of the investments for investments considered Level 2 inputs.

[5] This category represents cash and investments in various money market funds.

[6] The plan assets are invested in investment funds that hold a diversified portfolio of U.S and international equity securities and fixed income securities such as corporate bonds, government bonds, mortgage and asset-backed securities. The fair value of assets in this category is estimated using the net asset value per share of the investments.

[7] The Company considers the fair value of publicly traded registered investment funds to be a Level 1 input within the fair value hierarchy. In the above tables, the Company has revised the previous classification of publicly traded registered investment funds ($220.7 as of December 31, 2011) from Level 2 to Level 1.