Magento 2 get Parameters in the URL

First, you need to inject \Magento\Framework\App\Request\Http at _construct function then using

Magento2 how to getRequest

$this->request->getParam('id'),you can your data

protected $request;
    public function __construct(
        \Magento\Framework\App\Request\Http $request,
        ....//rest of parameters here
    ) {
       $this->request = $request;
       ...//rest of constructor here
    }
    public function getIddata()
    {
    // use 
    $this->request->getParams(); // all params
        return $this->request->getParam('id');
    }

You are trying in correct way.

 $custId = $this->getRequest()->getParam('id');

You can try with below code also

 $params = $this->request->getParams();
 $custId = $params['id'];