Fair Value Measurements, Fair Value Hierarchy Table (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Financial Assets:
Derivative Asset	$ 85.7		$ 81.8
Deferred compensation plan assets	7.3		6.5
Investment Percentage in Industrial Sector	51.00%		56.00%
Investment Percentage in Financial Sector	37.00%		35.00%
Investment Percentage in Utilities Sector	12.00%		9.00%
Financial Liabilities:
Derivative Liabilities	(96.8)		(86.1)
Fair Value, Measurements, Recurring [Member]
Financial Assets:
Cash and cash equivalents	177.7	[1]	169.5	[1]
Deferred compensation plan assets	7.3		6.5
Total Assets	1,171.1		1,158.2
Financial Liabilities:
Convertible Notes, including Bifurcated Conversion Feature	(263.3)		(260.0)
Total Liabilities	(604.6)		(601.5)
Fair Value, Measurements, Recurring [Member] | VEBAs and Canadian Pension Plan | Fixed income investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	394.3	[2]	375.0	[2]
Fair Value, Measurements, Recurring [Member] | VEBAs and Canadian Pension Plan | Mortgage backed securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	30.1		25.9
Fair Value, Measurements, Recurring [Member] | VEBAs and Canadian Pension Plan | Corporate debt securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	75.4	[3]	78.2	[3]
Fair Value, Measurements, Recurring [Member] | VEBAs and Canadian Pension Plan | Equity investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	191.3	[4]	175.3	[4]
Fair Value, Measurements, Recurring [Member] | VEBAs and Canadian Pension Plan | United States Treasuries
Financial Assets:
VEBAs and Canadian Pension Plan Assets	39.5		43.3
Fair Value, Measurements, Recurring [Member] | VEBAs and Canadian Pension Plan | Municipal debt securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	1.8		1.6
Fair Value, Measurements, Recurring [Member] | VEBAs and Canadian Pension Plan | Cash and money market investments
Financial Assets:
VEBAs and Canadian Pension Plan Assets	19.3	[5]	36.8	[5]
Fair Value, Measurements, Recurring [Member] | VEBAs and Canadian Pension Plan | Asset backed securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	8.1		8.5
Fair Value, Measurements, Recurring [Member] | VEBAs and Canadian Pension Plan | Diversified investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	26.6	[6]	26.3	[6]
Fair Value, Measurements, Recurring [Member] | Senior Notes
Financial Liabilities:
Senior Notes	(244.5)		(255.4)
Fair Value, Measurements, Recurring [Member] | Debt Securities
Financial Assets:
Short-term investments	114.0		129.5
Fair Value, Measurements, Recurring [Member] | Aluminum | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset			0.1
Financial Liabilities:
Derivative Liabilities	(4.2)		(1.8)
Fair Value, Measurements, Recurring [Member] | Aluminum | Midwest premium swap contracts
Financial Assets:
Derivative Asset	1.0		1.1
Fair Value, Measurements, Recurring [Member] | Natural Gas | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset			0.5
Financial Liabilities:
Derivative Liabilities	(6.2)		(0.8)
Fair Value, Measurements, Recurring [Member] | Electricity | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset			0.5
Financial Liabilities:
Derivative Liabilities	(1.7)		(0.4)
Fair Value, Measurements, Recurring [Member] | Foreign Currency | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset			0.1
Fair Value, Measurements, Recurring [Member] | Hedges Relating to the Convertible Notes | Call Options
Financial Assets:
Derivative Asset	84.7		79.5
Fair Value, Measurements, Recurring [Member] | Hedges Relating to the Convertible Notes | Bifurcated Conversion Feature
Financial Liabilities:
Derivative Liabilities	(84.7)		(83.1)
Fair Value, Measurements, Recurring [Member] | Level 1
Financial Assets:
Cash and cash equivalents	29.5		57.7	[1]
Deferred compensation plan assets	0		0
Total Assets	123.2		171.6
Financial Liabilities:
Convertible Notes, including Bifurcated Conversion Feature	(263.3)		(260.0)
Total Liabilities	(507.8)		(515.4)
Fair Value, Measurements, Recurring [Member] | Level 1 | VEBAs and Canadian Pension Plan | Fixed income investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	54.0	[2]	57.0	[2]
Fair Value, Measurements, Recurring [Member] | Level 1 | VEBAs and Canadian Pension Plan | Mortgage backed securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Fair Value, Measurements, Recurring [Member] | Level 1 | VEBAs and Canadian Pension Plan | Corporate debt securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Fair Value, Measurements, Recurring [Member] | Level 1 | VEBAs and Canadian Pension Plan | Equity investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0	[4]
Fair Value, Measurements, Recurring [Member] | Level 1 | VEBAs and Canadian Pension Plan | United States Treasuries
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Fair Value, Measurements, Recurring [Member] | Level 1 | VEBAs and Canadian Pension Plan | Municipal debt securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Fair Value, Measurements, Recurring [Member] | Level 1 | VEBAs and Canadian Pension Plan | Cash and money market investments
Financial Assets:
VEBAs and Canadian Pension Plan Assets	19.3	[5]	36.8	[5]
Fair Value, Measurements, Recurring [Member] | Level 1 | VEBAs and Canadian Pension Plan | Asset backed securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Fair Value, Measurements, Recurring [Member] | Level 1 | VEBAs and Canadian Pension Plan | Diversified investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	20.4	[6]	20.1	[6]
Fair Value, Measurements, Recurring [Member] | Level 1 | Senior Notes
Financial Liabilities:
Senior Notes	(244.5)		(255.4)
Fair Value, Measurements, Recurring [Member] | Level 1 | Debt Securities
Financial Assets:
Short-term investments	0		0
Fair Value, Measurements, Recurring [Member] | Level 1 | Aluminum | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset			0
Financial Liabilities:
Derivative Liabilities	0		0
Fair Value, Measurements, Recurring [Member] | Level 1 | Aluminum | Midwest premium swap contracts
Financial Assets:
Derivative Asset	0		0
Fair Value, Measurements, Recurring [Member] | Level 1 | Natural Gas | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset			0
Financial Liabilities:
Derivative Liabilities	0		0
Fair Value, Measurements, Recurring [Member] | Level 1 | Electricity | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset			0
Financial Liabilities:
Derivative Liabilities	0		0
Fair Value, Measurements, Recurring [Member] | Level 1 | Foreign Currency | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset			0
Fair Value, Measurements, Recurring [Member] | Level 1 | Hedges Relating to the Convertible Notes | Call Options
Financial Assets:
Derivative Asset	0		0
Fair Value, Measurements, Recurring [Member] | Level 1 | Hedges Relating to the Convertible Notes | Bifurcated Conversion Feature
Financial Liabilities:
Derivative Liabilities	0		0
Fair Value, Measurements, Recurring [Member] | Level 2
Financial Assets:
Cash and cash equivalents	148.2		111.8	[1]
Short-term investments	114.0
Deferred compensation plan assets	7.3		6.5
Total Assets	1,046.9		985.5
Financial Liabilities:
Convertible Notes, including Bifurcated Conversion Feature	0		0
Total Liabilities	(96.8)		(86.1)
Fair Value, Measurements, Recurring [Member] | Level 2 | VEBAs and Canadian Pension Plan | Fixed income investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	340.3	[2]	318.0	[2]
Fair Value, Measurements, Recurring [Member] | Level 2 | VEBAs and Canadian Pension Plan | Mortgage backed securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	30.1		25.9
Fair Value, Measurements, Recurring [Member] | Level 2 | VEBAs and Canadian Pension Plan | Corporate debt securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	75.4	[3]	78.2	[3]
Fair Value, Measurements, Recurring [Member] | Level 2 | VEBAs and Canadian Pension Plan | Equity investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	191.3	[4]	175.3	[4]
Fair Value, Measurements, Recurring [Member] | Level 2 | VEBAs and Canadian Pension Plan | United States Treasuries
Financial Assets:
VEBAs and Canadian Pension Plan Assets	39.5		43.3
Fair Value, Measurements, Recurring [Member] | Level 2 | VEBAs and Canadian Pension Plan | Municipal debt securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	1.8		1.6
Fair Value, Measurements, Recurring [Member] | Level 2 | VEBAs and Canadian Pension Plan | Cash and money market investments
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Fair Value, Measurements, Recurring [Member] | Level 2 | VEBAs and Canadian Pension Plan | Asset backed securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	8.1		8.5
Fair Value, Measurements, Recurring [Member] | 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]	6.2	[6]
Fair Value, Measurements, Recurring [Member] | Level 2 | Senior Notes
Financial Liabilities:
Senior Notes	0		0
Fair Value, Measurements, Recurring [Member] | Level 2 | Debt Securities
Financial Assets:
Short-term investments			129.5
Fair Value, Measurements, Recurring [Member] | Level 2 | Aluminum | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset			0.1
Financial Liabilities:
Derivative Liabilities	(4.2)		(1.8)
Fair Value, Measurements, Recurring [Member] | Level 2 | Aluminum | Midwest premium swap contracts
Financial Assets:
Derivative Asset	0		0
Fair Value, Measurements, Recurring [Member] | Level 2 | Natural Gas | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset			0.5
Financial Liabilities:
Derivative Liabilities	(6.2)		(0.8)
Fair Value, Measurements, Recurring [Member] | Level 2 | Electricity | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset			0.5
Financial Liabilities:
Derivative Liabilities	(1.7)		(0.4)
Fair Value, Measurements, Recurring [Member] | Level 2 | Foreign Currency | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset			0.1
Fair Value, Measurements, Recurring [Member] | Level 2 | Hedges Relating to the Convertible Notes | Call Options
Financial Assets:
Derivative Asset	84.7		79.5
Fair Value, Measurements, Recurring [Member] | Level 2 | Hedges Relating to the Convertible Notes | Bifurcated Conversion Feature
Financial Liabilities:
Derivative Liabilities	(84.7)		(83.1)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Assets:
Cash and cash equivalents	0		0
Deferred compensation plan assets	0		0
Total Assets	1.0		1.1
Financial Liabilities:
Convertible Notes, including Bifurcated Conversion Feature	0		0
Total Liabilities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | VEBAs and Canadian Pension Plan | Fixed income investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | VEBAs and Canadian Pension Plan | Mortgage backed securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | VEBAs and Canadian Pension Plan | Corporate debt securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | VEBAs and Canadian Pension Plan | Equity investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | VEBAs and Canadian Pension Plan | United States Treasuries
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | VEBAs and Canadian Pension Plan | Municipal debt securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | VEBAs and Canadian Pension Plan | Cash and money market investments
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | VEBAs and Canadian Pension Plan | Asset backed securities
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | VEBAs and Canadian Pension Plan | Diversified investment funds in registered investment companies
Financial Assets:
VEBAs and Canadian Pension Plan Assets	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Senior Notes
Financial Liabilities:
Senior Notes	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Debt Securities
Financial Assets:
Short-term investments	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Aluminum | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset			0
Financial Liabilities:
Derivative Liabilities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Aluminum | Midwest premium swap contracts
Financial Assets:
Derivative Asset			1.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Natural Gas | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset			0
Financial Liabilities:
Derivative Liabilities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Electricity | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset			0
Financial Liabilities:
Derivative Liabilities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Foreign Currency | Fixed priced contracts | Purchase
Financial Assets:
Derivative Asset			0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Hedges Relating to the Convertible Notes | Call Options
Financial Assets:
Derivative Asset	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Hedges Relating to the Convertible Notes | Bifurcated Conversion Feature
Financial Liabilities:
Derivative Liabilities	0		0
Income Approach Valuation Technique | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Aluminum | Midwest premium swap contracts
Financial Assets:
Derivative Asset	$ 1.0

[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 2014 represented approximately 51%, 37% and 12% of the total portfolio in this category, respectively. Investments in the industrial, financial and utilities sectors in 2013 represented approximately 56%, 35% 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 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.