This excerpt taken from the MRO DEF 14A filed Mar 10, 2005.
Obligations Associated with Financings
Marathon remains obligated (primarily or contingently) for certain debt and other financial arrangements for which United States Steel has assumed responsibility for repayment under the terms of the separation. As of December 31, 2004, Marathon has identified $671 million financial obligations, which have been assumed by United States Steel. These financial obligations will continue in 2005.