Fair Value Measurements, Fair Value Hierarchy Table (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Financial Assets:
Derivative Asset	$ 81.8		$ 58.5
Deferred compensation plan assets	6.5		5.6
Investment Percentage in Industrial Sector	56.00%		61.00%
Investment Percentage in Financial Sector	35.00%		33.00%
Investment Percentage in Utilities Sector	9.00%		6.00%
Financial Liabilities:
Derivative Liabilities	(86.1)		(66.7)
Recurring
Financial Assets:
Cash and cash equivalents	169.5	[1]	273.4	[1]
Deferred compensation plan assets	6.5		5.6
Total Assets	1,158.2		1,152.9
Financial Liabilities:
Convertible Notes	(260.0)		(240.1)
Total Liabilities	(601.5)		(556.8)
Recurring | VEBAs and Canadian Pension Plan | Fixed income investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	375.0	[2]	427.7	[2]
Recurring | VEBAs and Canadian Pension Plan | Mortgage backed securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	25.9		31.5
Recurring | VEBAs and Canadian Pension Plan | Corporate debt securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	78.2	[3]	40.4	[3]
Recurring | VEBAs and Canadian Pension Plan | Equity investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	175.3	[4]	172.9	[4]
Recurring | VEBAs and Canadian Pension Plan | United States Treasuries
Financial Assets:
VEBAs and Canadian Pension Plan Assets	43.3		13.6
Recurring | VEBAs and Canadian Pension Plan | Municipal debt securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	1.6		3.9
Recurring | VEBAs and Canadian Pension Plan | Cash and money market investments
Financial Assets:
VEBAs and Canadian Pension Plan Assets	36.8	[5]	16.4	[5]
Recurring | VEBAs and Canadian Pension Plan | Asset backed securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	8.5		3.2
Recurring | VEBAs and Canadian Pension Plan | Diversified investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	26.3	[6]	12.1	[6]
Recurring | VEBAs and Canadian Pension Plan | Equity Securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets			8.7
Recurring | Senior Notes
Financial Liabilities:
Senior Notes	(255.4)		(250.0)
Recurring | Debt Securities
Financial Assets:
Short-term investments	129.5		85.0
Recurring | Aluminum | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset	0.1		2.6
Financial Liabilities:
Derivative Liabilities	(1.8)		(0.5)
Recurring | Aluminum | Midwest premium swap contracts
Financial Assets:
Derivative Asset	1.1		0.4
Recurring | Natural Gas | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset	0.5		0.2
Financial Liabilities:
Derivative Liabilities	(0.8)		(2.6)
Recurring | Natural Gas | Option contracts | Sales
Financial Liabilities:
Derivative Liabilities			(0.5)
Recurring | Electricity | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset	0.5
Financial Liabilities:
Derivative Liabilities	(0.4)		(1.0)
Recurring | Foreign Currency | Fixed priced contracts | Purchase | Euro
Financial Assets:
Derivative Asset	0.1
Recurring | Hedges Relating to the Convertible Notes | Call Options
Financial Assets:
Derivative Asset	79.5		55.3
Recurring | Hedges Relating to the Convertible Notes | Bifurcated Conversion Feature
Financial Liabilities:
Derivative Liabilities	(83.1)		(62.1)
Recurring | Level 1
Financial Assets:
Cash and cash equivalents	57.7	[1]	107.9	[1]
Deferred compensation plan assets	0		0
Total Assets	171.6		445.8
Financial Liabilities:
Convertible Notes	(260.0)		(240.1)
Total Liabilities	(515.4)		(490.1)
Recurring | Level 1 | VEBAs and Canadian Pension Plan | Fixed income investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	57.0	[2]	192.3	[2]
Recurring | Level 1 | VEBAs and Canadian Pension Plan | Mortgage backed securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 1 | VEBAs and Canadian Pension Plan | Corporate debt securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 1 | VEBAs and Canadian Pension Plan | Equity investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		114.1	[4]
Recurring | Level 1 | VEBAs and Canadian Pension Plan | United States Treasuries
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 1 | VEBAs and Canadian Pension Plan | Municipal debt securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 1 | VEBAs and Canadian Pension Plan | Cash and money market investments
Financial Assets:
VEBAs and Canadian Pension Plan Assets	36.8	[5]	16.4	[5]
Recurring | Level 1 | VEBAs and Canadian Pension Plan | Asset backed securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 1 | VEBAs and Canadian Pension Plan | Diversified investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	20.1	[6]	6.4	[6]
Recurring | Level 1 | VEBAs and Canadian Pension Plan | Equity Securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets			8.7
Recurring | Level 1 | Senior Notes
Financial Liabilities:
Senior Notes	(255.4)		(250.0)
Recurring | Level 1 | Debt Securities
Financial Assets:
Short-term investments	0		0
Recurring | Level 1 | Aluminum | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset	0		0
Financial Liabilities:
Derivative Liabilities	0		0
Recurring | Level 1 | Aluminum | Midwest premium swap contracts
Financial Assets:
Derivative Asset	0		0
Recurring | Level 1 | Natural Gas | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset	0		0
Financial Liabilities:
Derivative Liabilities	0		0
Recurring | Level 1 | Natural Gas | Option contracts | Sales
Financial Liabilities:
Derivative Liabilities			0
Recurring | Level 1 | Electricity | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset	0
Financial Liabilities:
Derivative Liabilities	0		0
Recurring | Level 1 | Foreign Currency | Fixed priced contracts | Purchase | Euro
Financial Assets:
Derivative Asset	0
Recurring | Level 1 | Hedges Relating to the Convertible Notes | Call Options
Financial Assets:
Derivative Asset	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	111.8	[1]	165.5	[1]
Deferred compensation plan assets	6.5		5.6
Total Assets	985.5		706.7
Financial Liabilities:
Convertible Notes	0		0
Total Liabilities	(86.1)		(66.7)
Recurring | Level 2 | VEBAs and Canadian Pension Plan | Fixed income investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	318.0	[2]	235.4	[2]
Recurring | Level 2 | VEBAs and Canadian Pension Plan | Mortgage backed securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	25.9		31.5
Recurring | Level 2 | VEBAs and Canadian Pension Plan | Corporate debt securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	78.2	[3]	40.4	[3]
Recurring | Level 2 | VEBAs and Canadian Pension Plan | Equity investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	175.3	[4]	58.8	[4]
Recurring | Level 2 | VEBAs and Canadian Pension Plan | United States Treasuries
Financial Assets:
VEBAs and Canadian Pension Plan Assets	43.3		13.6
Recurring | Level 2 | VEBAs and Canadian Pension Plan | Municipal debt securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	1.6		3.9
Recurring | Level 2 | VEBAs and Canadian Pension Plan | Cash and money market investments
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 2 | VEBAs and Canadian Pension Plan | Asset backed securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	8.5		3.2
Recurring | Level 2 | VEBAs and Canadian Pension Plan | Diversified investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	6.2	[6]	5.7	[6]
Recurring | Level 2 | VEBAs and Canadian Pension Plan | Equity Securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets			0
Recurring | Level 2 | Senior Notes
Financial Liabilities:
Senior Notes	0		0
Recurring | Level 2 | Debt Securities
Financial Assets:
Short-term investments	129.5		85.0
Recurring | Level 2 | Aluminum | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset	0.1		2.6
Financial Liabilities:
Derivative Liabilities	(1.8)		(0.5)
Recurring | Level 2 | Aluminum | Midwest premium swap contracts
Financial Assets:
Derivative Asset	0		0
Recurring | Level 2 | Natural Gas | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset	0.5		0.2
Financial Liabilities:
Derivative Liabilities	(0.8)		(2.6)
Recurring | Level 2 | Natural Gas | Option contracts | Sales
Financial Liabilities:
Derivative Liabilities			(0.5)
Recurring | Level 2 | Electricity | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset	0.5
Financial Liabilities:
Derivative Liabilities	(0.4)		(1.0)
Recurring | Level 2 | Foreign Currency | Fixed priced contracts | Purchase | Euro
Financial Assets:
Derivative Asset	0.1
Recurring | Level 2 | Hedges Relating to the Convertible Notes | Call Options
Financial Assets:
Derivative Asset	79.5		55.3
Recurring | Level 2 | Hedges Relating to the Convertible Notes | Bifurcated Conversion Feature
Financial Liabilities:
Derivative Liabilities	(83.1)		(62.1)
Recurring | Level 3
Financial Assets:
Cash and cash equivalents	0		0
Deferred compensation plan assets	0		0
Total Assets	1.1		0.4
Financial Liabilities:
Convertible Notes	0		0
Total Liabilities	0		0
Recurring | Level 3 | VEBAs and Canadian Pension Plan | Fixed income investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 3 | VEBAs and Canadian Pension Plan | Mortgage backed securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 3 | VEBAs and Canadian Pension Plan | Corporate debt securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 3 | VEBAs and Canadian Pension Plan | Equity investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 3 | VEBAs and Canadian Pension Plan | United States Treasuries
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 3 | VEBAs and Canadian Pension Plan | Municipal debt securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 3 | VEBAs and Canadian Pension Plan | Cash and money market investments
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 3 | VEBAs and Canadian Pension Plan | Asset backed securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 3 | VEBAs and Canadian Pension Plan | Diversified investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Recurring | Level 3 | VEBAs and Canadian Pension Plan | Equity Securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets			0
Recurring | Level 3 | Senior Notes
Financial Liabilities:
Senior Notes	0		0
Recurring | Level 3 | Debt Securities
Financial Assets:
Short-term investments	0		0
Recurring | Level 3 | Aluminum | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset	0		0
Financial Liabilities:
Derivative Liabilities	0		0
Recurring | Level 3 | Aluminum | Midwest premium swap contracts
Financial Assets:
Derivative Asset	1.1		0.4
Recurring | Level 3 | Natural Gas | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset	0		0
Financial Liabilities:
Derivative Liabilities	0		0
Recurring | Level 3 | Natural Gas | Option contracts | Sales
Financial Liabilities:
Derivative Liabilities			0
Recurring | Level 3 | Electricity | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset	0
Financial Liabilities:
Derivative Liabilities	0		0
Recurring | Level 3 | Foreign Currency | Fixed priced contracts | Purchase | Euro
Financial Assets:
Derivative Asset	0
Recurring | Level 3 | Hedges Relating to the Convertible Notes | Call Options
Financial Assets:
Derivative Asset	0		0
Recurring | Level 3 | Hedges Relating to the Convertible Notes | Bifurcated Conversion Feature
Financial Liabilities:
Derivative Liabilities	$ 0		$ 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 (i) marketable fixed income securities such as (a) U.S. Treasury and other government and agency securities, (b) municipal bonds, (c) mortgage-backed securities, (d) asset-backed securities, (e) corporate bonds, notes and debentures in various sectors, (f) preferred and common stock, (g) investments in affiliated and other investment companies, (h) short-term investments and other net assets and (i) repurchase agreements and reverse repurchase agreements, (ii) other commingled investments, (iii) investment grade debt, (iv) fixed income instruments which may be represented by options, future contracts or swap agreements, and (v) cash and cash equivalents. 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 2013 represented approximately 56%, 35% and 9% of the total portfolio in this category, respectively. Investments in the industrial, financial and utilities sectors in 2012 represented approximately 61%, 33% and 6% 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 and equity-related securities of U.S. and non-U.S. issuers across all market capitalization, (ii) common stock in investment trust funds, and (iii) 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 (i) U.S and international debt and equity securities, (ii) fixed income securities such as corporate bonds and government bonds, (iii) mortgage-related securities, and (iv) cash and cash equivalents. The fair value of assets in this category is estimated using the net asset value per share of the investments.