Debt (Details) In Millions, except Share data, unless otherwise specified	12 Months Ended					12 Months Ended															12 Months Ended				12 Months Ended
	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2012 Foreign credit agreements [Member] USD ($)	Dec. 31, 2011 Foreign credit agreements [Member] USD ($)	Dec. 31, 2012 ATI 2019 Notes [Member] USD ($)	Dec. 31, 2011 ATI 2019 Notes [Member] USD ($)	Dec. 31, 2012 Allegheny Ludlum debentures due 2025 [Member] USD ($)	Dec. 31, 2011 Allegheny Ludlum debentures due 2025 [Member] USD ($)	Dec. 31, 2012 Industrial revenue bonds due through 2020 and other [Member] USD ($)	Dec. 31, 2011 Industrial revenue bonds due through 2020 and other [Member] USD ($)	Dec. 31, 2012 ATI 2014 Convertible Notes [Member] USD ($)	Dec. 31, 2011 ATI 2014 Convertible Notes [Member] USD ($)	Dec. 31, 2012 ATI 2021 Notes [Member] USD ($)	Dec. 31, 2011 ATI 2021 Notes [Member] USD ($)	Dec. 31, 2012 Ladish Series C Notes [Member] USD ($)	Dec. 31, 2011 Ladish Series C Notes [Member] USD ($)	Dec. 31, 2012 Ladish Series B Notes [Member] USD ($)	Dec. 31, 2011 Ladish Series B Notes [Member] USD ($)	Dec. 31, 2012 Seperateletter of Credit Facility [Member] USD ($)	Dec. 31, 2012 Domestic Bank Group $400 million unsecured credit agreement [Member] USD ($)	Dec. 31, 2011 Domestic Bank Group $400 million unsecured credit agreement [Member] USD ($)	Dec. 31, 2012 STAL Revolving Credit Facility [Member] USD ($)	Dec. 31, 2012 STAL Revolving Credit Facility [Member] CNY	Dec. 31, 2012 Foreign Credit Facilities [Member] USD ($)	Dec. 31, 2012 STAL Trade AP Financing [Member] USD ($)
Interest Costs Incurred [Abstract]
Interest Expense Debt	$ 72.4	$ 93.7	$ 63.8
Interest Costs Capitalized	24.5	12.1	12.5
Interest Costs Incurred	96.5	102.8	72.8
Investment Income Interest	0.8	1.4	1.1
Line Of Credit Facility [Line Items]
Lineof Credit Facility Amount Outstanding Including Lettersof Credit																					4.0
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, 2012, the leverage ratio was 2.09 and the interest coverage ratio was 5.68.
Line Of Credit Facility Borrowing Capacity Description																					The Company has a $400 million senior unsecured domestic revolving credit facility that expires in April 2017. 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																				32.0	0	0				0
Line Of Credit Facility Maximum Borrowing Capacity																					400.0		33.0	205.0	27.0
Line Of Credit Facility Commitment Fee Description																					In addition, the unsecured facility contains a facility fee of 0.15% to 0.25% 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, 2012, was 1.26%.
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	17.1
Long Term Debt Maturities Repayments Of Principal In Year Two	419.6
Long Term Debt Maturities Repayments Of Principal In Year Three	17.2
Long Term Debt Maturities Repayments Of Principal In Year Four	21.4
Long Term Debt Maturities Repayments Of Principal In Year Five	0.3
Debt Instrument [Line Items]
Debt Instrument Issuer						Allegheny Technologies	Allegheny Technologies	Allegheny Ludlum	Allegheny Ludlum			Allegheny Technologies	Allegheny Technologies	Allegheny Technologies	Allegheny Technologies	ATI Ladish, LLC	ATI Ladish, LLC Series C	ATI Ladish, LLC	ATI Ladish, LLC Series B
Debt Instrument Carrying Amount				14.2	24.5	350.0	350.0	150.0	150.0	6.1	5.9	402.5	402.5	500.0	500.0	32.5	44.6	24.8	31.8
Debt Instrument Maturity Date						Jun. 01, 2019	Jun. 01, 2019	Dec. 15, 2025	Dec. 15, 2025			Jun. 01, 2014	Jun. 01, 2014	Jan. 15, 2021	Jan. 15, 2021	Sep. 02, 2015	Sep. 02, 2015	May 16, 2016	May 16, 2016
Debt Instrument Maturity Date Range End										Jan. 01, 2020	Jan. 01, 2020
Debt Instrument Interest Rate Stated Percentage				1.26%		9.375%	9.375%	6.95%	6.95%			4.25%	4.25%	5.95%	5.95%	6.41%	6.41%	6.14%	6.14%
Total short-term and long-term debt	1,480.1	1,509.3
Debt Current	17.1	27.3
Long-term debt	1,463.0	1,482.0
Issuances of long-term debt	0	500.0	0
Debt issuance costs	0	5.0	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	16.7	143.8	11.3
Debt Instrument Outstanding Face Amount																30.0		22.9
Business Acquisition Purchase Price Allocation Notes Payableand L T Debt																$ 2.5	$ 4.6	$ 1.9	$ 3.2