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Business Segments (Details4) (USD $) In Millions, unless otherwise specified	3 Months Ended										12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales	$ 1,047.5us-gaap_SalesRevenueGoodsNet		$ 1,069.6us-gaap_SalesRevenueGoodsNet	$ 1,119.0us-gaap_SalesRevenueGoodsNet	$ 987.3us-gaap_SalesRevenueGoodsNet	$ 915.3us-gaap_SalesRevenueGoodsNet		$ 972.4us-gaap_SalesRevenueGoodsNet	$ 1,056.8us-gaap_SalesRevenueGoodsNet	$ 1,099.0us-gaap_SalesRevenueGoodsNet	$ 4,223.4us-gaap_SalesRevenueGoodsNet		$ 4,043.5us-gaap_SalesRevenueGoodsNet		$ 4,666.9us-gaap_SalesRevenueGoodsNet
Identifiable Assets	6,582.6us-gaap_Assets					6,898.5us-gaap_Assets					6,582.6us-gaap_Assets		6,898.5us-gaap_Assets		6,247.8us-gaap_Assets
Percent of total	100.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount					100.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount					100.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount		100.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount		100.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Identifiable Assets	5,879.6us-gaap_Assets / us-gaap_StatementGeographicalAxis = country_US					6,145.4us-gaap_Assets / us-gaap_StatementGeographicalAxis = country_US					5,879.6us-gaap_Assets / us-gaap_StatementGeographicalAxis = country_US		6,145.4us-gaap_Assets / us-gaap_StatementGeographicalAxis = country_US		5,505.0us-gaap_Assets / us-gaap_StatementGeographicalAxis = country_US
Percent of total	90.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = country_US					89.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = country_US					90.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = country_US		89.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = country_US		88.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = country_US
United Kingdom [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Identifiable Assets	196.3us-gaap_Assets / us-gaap_StatementGeographicalAxis = country_GB					208.0us-gaap_Assets / us-gaap_StatementGeographicalAxis = country_GB					196.3us-gaap_Assets / us-gaap_StatementGeographicalAxis = country_GB		208.0us-gaap_Assets / us-gaap_StatementGeographicalAxis = country_GB		239.2us-gaap_Assets / us-gaap_StatementGeographicalAxis = country_GB
Percent of total	3.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = country_GB					3.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = country_GB					3.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = country_GB		3.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = country_GB		4.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = country_GB
China [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Identifiable Assets	280.5us-gaap_Assets / us-gaap_StatementGeographicalAxis = country_CN					258.1us-gaap_Assets / us-gaap_StatementGeographicalAxis = country_CN					280.5us-gaap_Assets / us-gaap_StatementGeographicalAxis = country_CN		258.1us-gaap_Assets / us-gaap_StatementGeographicalAxis = country_CN		276.2us-gaap_Assets / us-gaap_StatementGeographicalAxis = country_CN
Percent of total	4.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = country_CN					4.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = country_CN					4.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = country_CN		4.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = country_CN		4.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = country_CN
Luxembourg [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Identifiable Assets	81.8us-gaap_Assets / us-gaap_StatementGeographicalAxis = country_LU	[1]				145.9us-gaap_Assets / us-gaap_StatementGeographicalAxis = country_LU	[1]				81.8us-gaap_Assets / us-gaap_StatementGeographicalAxis = country_LU	[1]	145.9us-gaap_Assets / us-gaap_StatementGeographicalAxis = country_LU	[1]	48.3us-gaap_Assets / us-gaap_StatementGeographicalAxis = country_LU	[1]
Percent of total	1.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = country_LU	[1]				2.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = country_LU	[1]				1.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = country_LU	[1]	2.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = country_LU	[1]	1.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = country_LU	[1]
Other [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Identifiable Assets	144.4us-gaap_Assets / us-gaap_StatementGeographicalAxis = ati_OtherCountriesMember					141.1us-gaap_Assets / us-gaap_StatementGeographicalAxis = ati_OtherCountriesMember					144.4us-gaap_Assets / us-gaap_StatementGeographicalAxis = ati_OtherCountriesMember		141.1us-gaap_Assets / us-gaap_StatementGeographicalAxis = ati_OtherCountriesMember		179.1us-gaap_Assets / us-gaap_StatementGeographicalAxis = ati_OtherCountriesMember
Percent of total	2.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = ati_OtherCountriesMember					2.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = ati_OtherCountriesMember					2.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = ati_OtherCountriesMember		2.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = ati_OtherCountriesMember		3.00%ati_EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount / us-gaap_StatementGeographicalAxis = ati_OtherCountriesMember
External Sales [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales											4,223.4us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember		4,043.5us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember		4,666.9us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember
Percent of total											100.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember		100.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember		100.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember
External Sales [Member] | United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales											2,615.9us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_US		2,458.4us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_US		2,961.1us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_US
Percent of total											62.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_US		61.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_US		63.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_US
External Sales [Member] | United Kingdom [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales											228.4us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_GB		251.5us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_GB		303.9us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_GB
Percent of total											5.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_GB		6.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_GB		7.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_GB
External Sales [Member] | China [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales											249.6us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_CN		237.7us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_CN		255.4us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_CN
Percent of total											6.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_CN		6.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_CN		5.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_CN
External Sales [Member] | Germany [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales											207.7us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_DE		215.4us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_DE		256.0us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_DE
Percent of total											5.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_DE		5.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_DE		6.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_DE
External Sales [Member] | France [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales											168.1us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_FR		152.8us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_FR		157.0us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_FR
Percent of total											4.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_FR		4.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_FR		3.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_FR
External Sales [Member] | Canada [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales											147.0us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_CA		141.0us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_CA		134.9us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_CA
Percent of total											3.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_CA		4.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_CA		3.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_CA
External Sales [Member] | Italy [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales											160.7us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_IT		132.3us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_IT		136.1us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_IT
Percent of total											4.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_IT		3.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_IT		3.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_IT
External Sales [Member] | Japan [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales											89.3us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_JP		124.7us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_JP		93.7us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_JP
Percent of total											2.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_JP		3.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_JP		2.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_JP
External Sales [Member] | Mexico [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales											76.5us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_MX		54.9us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_MX		49.3us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_MX
Percent of total											2.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_MX		1.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_MX		1.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = country_MX
External Sales [Member] | Other [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales											$ 280.2us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = ati_OtherCountriesMember		$ 274.8us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = ati_OtherCountriesMember		$ 319.5us-gaap_SalesRevenueGoodsNet / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = ati_OtherCountriesMember
Percent of total											7.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = ati_OtherCountriesMember		7.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = ati_OtherCountriesMember		7.00%ati_EntityWideDisclosureOnGeographicAreasRevenueFromExternalCustomersAttributedToIndividualForeignCountriesPercentageAmount / us-gaap_MajorCustomersAxis = ati_ExternalCustomersMember / us-gaap_StatementGeographicalAxis = ati_OtherCountriesMember
[1] Comprises assets held by the Company’s European Treasury Center operation.

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