* interest on variable rate debt was calculated using the interest rate at year-end 2016 . as of december 31 , 2016 , our gross liability for uncertain tax positions was $ 76 million . we are not able to reasonably estimate the amount by which the liability will increase or decrease over an extended period of time or whether a cash settlement of the liability will be required . therefore , these amounts have been excluded from the schedule of contractual obligations. .