Debt (Details) In Millions, except Share data, unless otherwise specified	12 Months Ended					12 Months Ended									12 Months Ended								12 Months Ended				12 Months Ended
	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2011 Foreign credit agreements [Member] USD ($)	Dec. 31, 2010 Foreign credit agreements [Member] USD ($)	Dec. 31, 2011 ATI 2019 Notes [Member] USD ($)	Dec. 31, 2010 ATI 2019 Notes [Member] USD ($)	Dec. 31, 2011 ATI 2011 Notes [Member] USD ($)	Dec. 31, 2010 ATI 2011 Notes [Member] USD ($)	Dec. 31, 2009 ATI 2011 Notes [Member] USD ($)	Dec. 31, 2011 Allegheny Ludlum debentures due 2025 [Member] USD ($)	Dec. 31, 2010 Allegheny Ludlum debentures due 2025 [Member] USD ($)	Dec. 31, 2011 Promissory Note for J&L asset acquisition USD ($)	Dec. 31, 2010 Promissory Note for J&L asset acquisition USD ($)	Dec. 31, 2011 Industrial revenue bonds due through 2020 and other USD ($)	Dec. 31, 2010 Industrial revenue bonds due through 2020 and other USD ($)	Dec. 31, 2011 ATI 2014 Convertible Notes USD ($)	Dec. 31, 2010 ATI 2014 Convertible Notes USD ($)	Dec. 31, 2011 ATI 2021 Notes [Member] USD ($)	Dec. 31, 2011 Ladish Series C Notes [Member] USD ($)	Dec. 31, 2011 Ladish Series B Notes [Member] USD ($)	Dec. 31, 2011 Seperateletter of Credit Facility [Member] USD ($)	Dec. 31, 2011 Domestic Bank Group $400 million unsecured credit agreement [Member] USD ($)	Dec. 31, 2010 Domestic Bank Group $400 million unsecured credit agreement [Member] USD ($)	Dec. 31, 2011 STAL Revolving Credit Facility [Member] USD ($)	Dec. 31, 2011 STAL Revolving Credit Facility [Member] CNY	Dec. 31, 2011 Foreign Credit Facilities [Member] USD ($)	Dec. 31, 2011 STAL Trade AP Financing [Member] USD ($)
Extinguishment of Debt [Line Items]
Debt extinguishment costs	$ 0	$ 0	$ (9.2)
Interest Costs Incurred Abstract
Interest Expense Debt	93.7	63.8	21.4
Interest Costs Capitalized	12.1	12.5	39.0
Interest Costs Incurred	102.8	72.8	58.1
Investment Income Interest	1.4	1.1	2.1
Line Of Credit Facility [Line Items]
Lineof Credit Facility Amount Outstanding Including Lettersof Credit																							7.0
Line Of Credit Facility Covenant Terms																							The facility requires the Company to maintain a leverage ratio (consolidated total indebtedness divided by consolidated earnings before interest, taxes and depreciation and amortization) of not greater than 3.25, and maintain an interest coverage ratio (consolidated earnings before interest and taxes divided by interest expense) of not less than 2.0.
Line Of Credit Facility Covenant Compliance																							At December 31, 2011, the leverage ratio was 1.78 and the interest coverage ratio was 5.31.
Line Of Credit Facility Borrowing Capacity Description																							The Company has a $400 million senior unsecured domestic revolving credit facility that expires in December 2015. The facility includes a $200 million sublimit for the issuance of letters of credit. Under the terms of the facility, the Company may increase the size of the credit facility by up to $100 million without seeking the further approval of the lending group.
Minority Interest Ownership Percentage By Parent																									60.00%	60.00%
Line Of Credit Facility Amount Outstanding																						31.0	0	0				11.0
Line Of Credit Facility Maximum Borrowing Capacity																							400.0		32.0	205.0	37.0
Line Of Credit Facility Commitment Fee Description																							In addition, the unsecured facility contains a facility fee of 0.25% to 0.50% depending upon the value of the leverage ratio. The Company’s overall borrowing costs under the unsecured facility are not affected by changes in the Company’s credit ratings.				These agreements provide for annual facility fees of up to 0.20%.
Line Of Credit Facility Interest Rate Description																											The weighted average interest rate of foreign credit agreements as of December 31, 2011, was 1.60%.
Line Of Credit Facility Expiration Date																							December 2015
Line Of Credit Facility Remaining Borrowing Capacity																											13.0
Long Term Debt By Maturity Abstract
Long Term Debt Maturities Repayments Of Principal In Next Twelve Months	27.3
Long Term Debt Maturities Repayments Of Principal In Year Two	30.7
Long Term Debt Maturities Repayments Of Principal In Year Three	419.3
Long Term Debt Maturities Repayments Of Principal In Year Four	16.9
Long Term Debt Maturities Repayments Of Principal In Year Five	7.0
Debt Instrument [Line Items]
Debt Instrument Issuer						Allegheny Technologies	Allegheny Technologies	Allegheny Technologies	Allegheny Technologies		Allegheny Ludlum	Allegheny Ludlum					Allegheny Technologies	Allegheny Technologies	Allegheny Technologies	ATI Ladish, LLC	ATI Ladish, LLC
Debt Instrument Carrying Amount				24.5	26.3	350.0	350.0	0	117.3		150.0	150.0	0	10.2	5.9	7.0	402.5	402.5	500.0	44.6	31.8
Debt Instrument Maturity Date						Jun. 01, 2019	Jun. 01, 2019	Dec. 15, 2011	Dec. 15, 2011		Dec. 15, 2025	Dec. 15, 2025					Jun. 01, 2014	Jun. 01, 2014	Jan. 15, 2021	Sep. 02, 2015	May 16, 2016
Debt Instrument Maturity Date Range End															2020-01-01	2020-01-01
Debt Instrument Interest Rate Stated Percentage				1.60%		9.375%	9.375%	8.375%	8.375%		6.95%	6.95%					4.25%	4.25%	5.95%	6.41%	6.14%
Total short-term and long-term debt	1,509.3	1,063.3
Debt Current	27.3	141.4
Long-term debt	1,482.0	921.9
Deferred Gain Loss On Discontinuation Of Interest Rate Fair Value Hedge									0.9
Issuances of long-term debt	500.0	0	752.5															390.2	495.0
Debt issuance costs	5.0	0	18.1															12.3	5.0
Debt Instrument Convertible Number Of Equity Instruments																	9,630,336
Debt Instrument Convertible Conversion Ratio																	23.9263
Debt Instrument Convertible Conversion Price1																	$ 41.795
Payments on long-term debt and capital leases	143.8	11.3	194.6						183.3
Amortization Of Settled Interest Rate Swap								0.9	1.3	2.0
Debt Instrument Outstanding Face Amount																				40.0	28.6
Business Acquisition Purchase Price Allocation Notes Payableand L T Debt																				$ 4.6	$ 3.2