Debt (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended					6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended		6 Months Ended		6 Months Ended			6 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011	Jun. 30, 2012 Foreign credit agreements [Member]	Dec. 31, 2011 Foreign credit agreements [Member]	Jun. 30, 2012 ATI 2019 Notes [Member]	Dec. 31, 2011 ATI 2019 Notes [Member]	Jun. 30, 2012 Domestic Bank Group $400 million unsecured credit agreement [Member]	Dec. 31, 2011 Domestic Bank Group $400 million unsecured credit agreement [Member]	Jun. 30, 2012 Allegheny Ludlum debentures due 2025 [Member]	Dec. 31, 2011 Allegheny Ludlum debentures due 2025 [Member]	Jun. 30, 2012 Industrial revenue bonds due through 2020 and other [Member]	Dec. 31, 2011 Industrial revenue bonds due through 2020 and other [Member]	Jun. 30, 2012 ATI 2014 Convertible Notes [Member]	Dec. 31, 2011 ATI 2014 Convertible Notes [Member]	Jun. 30, 2012 ATI 2021 Notes [Member]	Dec. 31, 2011 ATI 2021 Notes [Member]	Jun. 30, 2012 Ladish Series C Notes [Member]	Dec. 31, 2011 Ladish Series C Notes [Member]	Jun. 30, 2012 Ladish Series B Notes [Member]	Dec. 31, 2011 Ladish Series B Notes [Member]	Jun. 30, 2012 Seperate Letter of Credit Facility [Member]	Jun. 30, 2012 Domestic Bank Group $400 million unsecured credit agreement [Member]	Dec. 31, 2011 Domestic Bank Group $400 million unsecured credit agreement [Member]	Jun. 30, 2012 STAL Revolving Credit Facility [Member]
Line Of Credit Facility [Line Items]
Line Of Credit Facility Covenant Terms																							This credit facility requires the Company to maintain a leverage ratio (consolidated total indebtedness net of cash on hand in excess of $50 million, divided by consolidated earnings before interest, taxes, depreciation and amortization, and non-cash pension expense) of not greater than 3.25, and maintain an interest coverage ratio (consolidated earnings before interest, taxes, and non-cash pension expense divided by interest expense) of not less than 2.0.
Line Of Credit Facility Covenant Compliance																							For the three months ended June 30, 2012, the leverage ratio was 2.05, and the interest coverage ratio was 5.58.
Foreign currency denomination	205 million renminbi
Line Of Credit Facility Collateral																									This credit facility is supported solely by STAL’s financial capability without any guarantees from the joint venture partners.
Minority Interest Ownership Percentage By Parent	60.00%
Line Of Credit Facility Amount Outstanding																						$ 32.0	$ 7.0
Line Of Credit Facility Maximum Borrowing Capacity																							400.0	400.0
Debt Instrument [Line Items]
Debt Instrument Issuer						Allegheny Technologies	Allegheny Technologies	Domestic Bank Group	Domestic Bank Group	Allegheny Ludlum	Allegheny Ludlum	Industrial revenue bonds, due through 2020, and other	Industrial revenue bonds, due through 2020, and other	Allegheny Technologies	Allegheny Technologies	Allegheny Technologies		ATI Ladish		ATI Ladish
Debt Instrument Carrying Amount				24.2	24.5	350.0	350.0	0	0	150.0	150.0	5.8	5.9	402.5	402.5	500.0	500.0	43.5	44.6	25.4	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		Sep. 02, 2015		May 16, 2016
Debt Instrument Maturity Date Range End												2020-01-01	2020-01-01
Debt Instrument Interest Rate Stated Percentage						9.375%	9.375%			6.95%	6.95%			4.25%	4.25%	5.95%		6.41%		6.14%
Total short-term and long-term debt	1,501.4		1,509.3
Debt Current	27.3		27.3
Long-term debt	1,474.1		1,482.0
Issuances of long-term debt	0	500.0
Debt issuance costs	0	5.0
Payments on long-term debt and capital leases	5.8	11.0
Debt Instrument Outstanding Face Amount																		40.0		22.9
Business Acquisition Purchase Price Allocation Notes Payableand L T Debt																		$ 3.5	$ 4.6	$ 2.5	$ 3.2