Debt Narrative (Details)		1 Months Ended		3 Months Ended	6 Months Ended
		Jul. 31, 2016 USD ($)	May 31, 2016	Jun. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 02, 2016 USD ($)	May 24, 2016 USD ($) $ / shares	Feb. 15, 2016	Dec. 31, 2015 USD ($)	Dec. 31, 2013
Debt Instrument [Line Items]
Debt issuance costs					$ 10,400,000	$ 0
Allegheny Technologies 5.875% Notes due 2023 (a)
Debt Instrument [Line Items]
Interest rate				7.875%	7.875%				7.875%	7.625%	5.875%
Additional annual interest expense to be incurred					$ 1,300,000
Outstanding borrowings	[1]			$ 500,000,000	500,000,000					$ 500,000,000
Domestic Bank Group $400 million asset-based credit facility
Debt Instrument [Line Items]
Debt issuance costs				900,000
Outstanding borrowings				0	0					0
Amount utilized to support the issuance of letters of credit				10,800,000	10,800,000
Average borrowings during period					$ 164,000,000
Interest rate during period					1.757%
Domestic Bank Group $400 million asset-based credit facility | Revolving credit facility
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 400,000,000	$ 400,000,000
Minimum fixed charge coverage ratio allowed in event of default				1	1
Minimum remaining borrowing capacity as a percent of maximum borrowing capacity				12.50%	12.50%
Line of Credit Facility, Remaining Borrowing Capacity				$ 62,500,000	$ 62,500,000
Minimum remaining borrowing capacity				40,000,000	40,000,000
Minimum required liquidity prior to maturity of 9.375% Senior Notes due 2019				500,000,000	$ 500,000,000
Minimum required liquidity number of days prior to maturity of 9.375% Senior Notes due 2019					91 days
Domestic Bank Group $400 million asset-based credit facility | Revolving credit facility | Minimum | LIBOR based borrowings
Debt Instrument [Line Items]
Variable interest rate (percentage)					2.00%
Domestic Bank Group $400 million asset-based credit facility | Revolving credit facility | Minimum | Base rate borrowings
Debt Instrument [Line Items]
Variable interest rate (percentage)					1.00%
Domestic Bank Group $400 million asset-based credit facility | Revolving credit facility | Maximum | LIBOR based borrowings
Debt Instrument [Line Items]
Variable interest rate (percentage)					2.50%
Domestic Bank Group $400 million asset-based credit facility | Revolving credit facility | Maximum | Base rate borrowings
Debt Instrument [Line Items]
Variable interest rate (percentage)					1.50%
Domestic Bank Group $400 million asset-based credit facility | Letter of credit sub-facility
Debt Instrument [Line Items]
Maximum borrowing capacity				200,000,000	$ 200,000,000
2017 Term Loan
Debt Instrument [Line Items]
Debt issuance costs				1,000,000
Outstanding borrowings				$ 100,000,000	100,000,000					0
2017 Term Loan | LIBOR based borrowings
Debt Instrument [Line Items]
Variable interest rate (percentage)				3.50%
Seperateletter of Credit Facility
Debt Instrument [Line Items]
Letters of credit outstanding				$ 32,000,000	$ 32,000,000
Allegheny Technologies, Convertible Senior Notes, 4.75%, Due 2022 [Member]
Debt Instrument [Line Items]
Interest rate				4.75%	4.75%
Outstanding borrowings				$ 287,500,000	$ 287,500,000					$ 0
Subsequent Event
Debt Instrument [Line Items]
Defined benefit plan contributions made		$ 115,000,000
Convertible Debt | Allegheny Technologies, Convertible Senior Notes, 4.75%, Due 2022 [Member]
Debt Instrument [Line Items]
Interest rate								4.75%
Long-term Debt							$ 37,500,000	$ 250,000,000
Debt issuance costs incurred				$ 9,400,000
Term of debt instrument				6 years
Conversion ratio			0.0692042
Number of shares issuable			19,896,194
Conversion price (in USD per share) | $ / shares								$ 14.45

[1] Bearing interest at 7.875% effective February 15, 2016.