I wouldn't worry about their debt as much. A few years from now, these debts at such low interest rates will be like an investment. I would not worry too much about debt with rates lower than inflation will very likely be. But they're paying off debt in the meantime at a nice steady pace. They're doing what they need to do.
They will get rid of their debt the old fashion way, paying it off. You have to realize that they generate close to $2 billion in free cash flow which includes the money that is written off to depreciation and amortization. Since the depreciation deduction is related to the debt used to buy the assets, it is reasonable that part of this free cash flow is used to pay down debt. CLF can easily pay $800 million a year against debt and be debt free in 5 years.