Gradle task which gathers all Detekt reports from the subprojects and put it in the one folder "$rootDir/reports/detekt". It simplifies CI process a bit.

detektGrabSubprojectsReports.groovy

task detektGrabSubprojectsReports {
    group = "Verification"

    def detektSingleReportFolder = "$rootDir/reports/detekt"
    def detektGeneralFolder = new File(detektSingleReportFolder)
    detektGeneralFolder.mkdirs();
    subprojects.findAll { subproject ->
        def projectReportDir = "$subproject.buildDir/reports"
        def detektReportFiles = [
                "detekt.xml",
                "detekt.html"
        ]
        def detektReport = new File("$projectReportDir/${detektReportFiles[0]}")
        if (detektReport.exists()) {
            println "Detekt report for $subproject is available."
            def subprojectReportDir = new File("$detektSingleReportFolder/${subproject.name}")
            subprojectReportDir.mkdirs()
            detektReportFiles.each { name ->
                println name
                def src = new File("$projectReportDir/$name")
                def target = new File("$subprojectReportDir/$name")
                target.createNewFile()
                target.write(src.text)
            }
        }
    }
}

kotlin version. I had to change (val projectReportDir = "${subproject.buildDir}/reports/detekt") for my project as the reports are in a detekt dir.

tasks {
    register("detektGrabSubprojectsReports") {
        group = "Verification"

        val detektSingleReportFolder = "${buildDir}/reports/detekt"
        val detektGeneralFolder = File(detektSingleReportFolder)
        detektGeneralFolder.mkdirs();
        subprojects.forEach { subproject ->
            val projectReportDir = "${subproject.buildDir}/reports/detekt"
            val detektReportFiles = listOf(
                    "detekt.xml",
                    "detekt.html"
            )
            val detektReport = File("${projectReportDir}/${detektReportFiles[0]}")
            if (detektReport.exists()) {
                println("Detekt report for $subproject is available.")
                val subprojectReportDir = File("${detektSingleReportFolder}/${subproject.name}")
                subprojectReportDir.mkdirs()
                detektReportFiles.forEach { name ->
                    println(name)
                    val src = File("${projectReportDir}/${name}")
                    val target = File("${subprojectReportDir}/${name}")
                    target.createNewFile()
                    target.writeText(src.readText())
                }
            }
        }
    }
}