Debt Narrative (Details)				9 Months Ended						9 Months Ended
	Sep. 30, 2013 Allegheny Technologies 5.875% Notes due 2023 USD ($)	Jul. 12, 2013 Allegheny Technologies 5.875% Notes due 2023 USD ($)	Dec. 31, 2012 Allegheny Technologies 5.875% Notes due 2023 USD ($)	Sep. 30, 2013 Domestic Bank Group $400 million unsecured credit facility USD ($)	Dec. 31, 2012 Domestic Bank Group $400 million unsecured credit facility USD ($)	Sep. 30, 2013 Seperateletter of Credit Facility USD ($)	Sep. 30, 2013 STAL Revolving Credit Facility USD ($)	Sep. 30, 2013 STAL Revolving Credit Facility CNY	Sep. 30, 2013 STAL Precision Stainless Steel Company Limited	Sep. 30, 2013 STAL Revolving Credit Facility
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 500,000,000
Debt Instrument, Interest Rate, Stated Percentage	5.875%
Line of Credit Facility, Maximum Borrowing Capacity				400,000,000			33,000,000	205,000,000
Line of Credit Facility, Borrowing Capacity Increase Limit				100,000,000
Debt Instrument, Covenant, Maximum Leverage Ratio, Period One				4.50
Debt Instrument, Covenant, Maximum Leverage Ratio, Period Two				4.00
Debt Instrument, Covenant, Maximum Leverage Ratio, Period Three				3.75
Debt Instrument, Covenant, Maximum Leverage Ratio, Period Four				3.50
Debt Instrument, Covenant, Maximum Interest Coverage Ratio, Period One				2.00
Debt Instrument, Covenant, Maximum Interest Coverage Ratio, Period Two				1.75
Debt Instrument, Covenant, Maximum Interest Coverage Ratio, Period Three				2.00
Debt Instrument, Covenant, Leverage Ratio				4.18
Debt Instrument, Covenant, Interest Coverage Ratio				2.71
Amount of Cash on Hand Used to Reduce the Indebtness Figure used in the Leverage Ratio Calculation				50,000,000
Long-term Debt, Gross	500,000,000		0	0	0
Line of Credit Facility, Amount Outstanding				4,000,000			0
Sublimit for letters of credit				200,000,000
Letters of Credit Outstanding, Amount						$ 32,000,000
Noncontrolling Interest, Ownership Percentage by Parent									60.00%
Line of Credit Facility, Expiration Date										Aug. 01, 2014