amount of commitment expiration per period other commercial commitments after millions total 2013 2014 2015 2016 2017 2017 .
what percentage of total commercial commitments are credit facilities?
[a] none of the credit facility was used as of december 31 , 2012 . [b] $ 100 million of the receivables securitization facility was utilized at december 31 , 2012 , which is accounted for as debt . the full program matures in july 2013 . [c] includes guaranteed obligations related to our headquarters building , equipment financings , and affiliated operations . [d] none of the letters of credit were drawn upon as of december 31 , 2012 . off-balance sheet arrangements guarantees 2013 at december 31 , 2012 , we were contingently liable for $ 307 million in guarantees . we have recorded a liability of $ 2 million for the fair value of these obligations as of december 31 , 2012 and 2011 . we entered into these contingent guarantees in the normal course of business , and they include guaranteed obligations related to our headquarters building , equipment financings , and affiliated operations . the final guarantee expires in 2022 . we are not aware of any existing event of default that would require us to satisfy these guarantees . we do not expect that these guarantees will have a material adverse effect on our consolidated financial condition , results of operations , or liquidity . other matters labor agreements 2013 approximately 86% ( 86 % ) of our 45928 full-time-equivalent employees are represented by 14 major rail unions . during the year , we concluded the most recent round of negotiations , which began in 2010 , with the ratification of new agreements by several unions that continued negotiating into 2012 . all of the unions executed similar multi-year agreements that provide for higher employee cost sharing of employee health and welfare benefits and higher wages . the current agreements will remain in effect until renegotiated under provisions of the railway labor act . the next round of negotiations will begin in early 2015 . inflation 2013 long periods of inflation significantly increase asset replacement costs for capital-intensive companies . as a result , assuming that we replace all operating assets at current price levels , depreciation charges ( on an inflation-adjusted basis ) would be substantially greater than historically reported amounts . derivative financial instruments 2013 we may use derivative financial instruments in limited instances to assist in managing our overall exposure to fluctuations in interest rates and fuel prices . we are not a party to leveraged derivatives and , by policy , do not use derivative financial instruments for speculative purposes . derivative financial instruments qualifying for hedge accounting must maintain a specified level of effectiveness between the hedging instrument and the item being hedged , both at inception and throughout the hedged period . we formally document the nature and relationships between the hedging instruments and hedged items at inception , as well as our risk-management objectives , strategies for undertaking the various hedge transactions , and method of assessing hedge effectiveness . changes in the fair market value of derivative financial instruments that do not qualify for hedge accounting are charged to earnings . we may use swaps , collars , futures , and/or forward contracts to mitigate the risk of adverse movements in interest rates and fuel prices ; however , the use of these derivative financial instruments may limit future benefits from favorable price movements . market and credit risk 2013 we address market risk related to derivative financial instruments by selecting instruments with value fluctuations that highly correlate with the underlying hedged item . we manage credit risk related to derivative financial instruments , which is minimal , by requiring high credit standards for counterparties and periodic settlements . at december 31 , 2012 and 2011 , we were not required to provide collateral , nor had we received collateral , relating to our hedging activities. .