2.2.0.25falsefalse074 - Statement - Aggregate amortization expense (Detail)truefalseIn Millionsfalse1falsefalseUSDfalsefalse10/1/2014 - 9/30/2015 USD ($) $c274_From1Oct2014To30Sep2015http://www.sec.gov/CIK0000353944duration2014-10-01T00:00:002015-09-30T00:00:00usdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$2falsefalseUSDfalsefalse10/1/2013 - 9/30/2014 USD ($) $c273_From1Oct2013To30Sep2014http://www.sec.gov/CIK0000353944duration2013-10-01T00:00:002014-09-30T00:00:00usdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$3falsefalseUSDfalsefalse10/1/2012 - 9/30/2013 USD ($) $c272_From1Oct2012To30Sep2013http://www.sec.gov/CIK0000353944duration2012-10-01T00:00:002013-09-30T00:00:00usdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$4falsefalseUSDfalsefalse10/1/2011 - 9/30/2012 USD ($) $c271_From1Oct2011To30Sep2012http://www.sec.gov/CIK0000353944duration2011-10-01T00:00:002012-09-30T00:00:00usdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$5falsefalseUSDfalsefalse10/1/2010 - 9/30/2011 USD ($) $c270_From1Oct2010To30Sep2011http://www.sec.gov/CIK0000353944duration2010-10-01T00:00:002011-09-30T00:00:00usdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$2true0igt_AggregateAmortizationExpenseAbstractigtfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalse4falsefalsefalse00falsefalsefalsefalsefalse5falsefalsefalse00falsefalsefalsefalsefalseOtherxbrli:stringItemTypestringNo definition available.falsefalseAggregate amortization expense [Abstract]3false0us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseus-gaaptruedebitdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalselabel1truefalsefalse2200000022.0falsetruefalsefalsefalse2truefalsefalse3090000030.9falsetruefalsefalsefalse3truefalsefalse3500000035.0falsetruefalsefalsefalse4truefalsefalse3840000038.4falsetruefalsefalsefalse5truefalsefalse4350000043.5falsetruefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryThe aggregate estimated amortization expense for each of the five succeeding fiscal years for intangible assets subject to amortization.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 142 -Paragraph 45 -Subparagraph a(3) falsefalseEstimated annual amortization52Aggregate amortization expense (Detail) (USD $)HundredThousandsUnKnownUnKnownUnKnownfalsetrue