Financial Instruments	3 Months Ended
Mar. 31, 2015
Financial Instruments[Abstract]
Financial Instruments	14. Financial Instruments Strategy and Risk – We may use derivative financial instruments in limited instances for other than trading purposes 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 interest rate and fuel price movements. Fair Value of Financial Instruments – The fair value of our short- and long-term debt was estimated using a market value price model, which utilizes applicable U.S. Treasury rates along with current market quotes on comparable debt securities. All of the inputs used to determine the fair market value of the Corporation’s long-term debt are Level 2 inputs and obtained from an independent source. At March 31, 2015, the fair value of total debt was $14.1 billion, approximately $1.8 billion more than the carrying value. At December 31, 2014, the fair value of total debt was $13.0 billion, approximately $1.5 billion more than the carrying value. The fair value of the Corporation’s debt is a measure of its current value under present market conditions. It does not impact the financial statements under current accounting rules. At both March 31, 2015, and December 31, 2014, approximately $163 million of debt securities contained call provisions that allow us to retire the debt instruments prior to final maturity, with the payment of fixed call premiums, or in certain cases, at par. The fair value of our cash equivalents approximates their carrying value due to the short-term maturities of these instruments.

14. Financial Instruments

Strategy and Risk – We may use derivative financial instruments in limited instances for other than trading purposes 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 interest rate and fuel price movements.

Fair Value of Financial Instruments – The fair value of our short- and long-term debt was estimated using a market value price model, which utilizes applicable U.S. Treasury rates along with current market quotes on comparable debt securities. All of the inputs used to determine the fair market value of the Corporation’s long-term debt are Level 2 inputs and obtained from an independent source. At March 31, 2015, the fair value of total debt was $14.1 billion, approximately $1.8 billion more than the carrying value. At December 31, 2014, the fair value of total debt was $13.0 billion, approximately $1.5 billion more than the carrying value. The fair value of the Corporation’s debt is a measure of its current value under present market conditions. It does not impact the financial statements under current accounting rules. At both March 31, 2015, and December 31, 2014, approximately $163 million of debt securities contained call provisions that allow us to retire the debt instruments prior to final maturity, with the payment of fixed call premiums, or in certain cases, at par. The fair value of our cash equivalents approximates their carrying value due to the short-term maturities of these instruments.