11. Financial Instruments

We utilize derivative financial instruments to manage exposure to certain risks related to our ongoing operations. The primary risks managed through the use of derivative instruments include interest rate risk, currency exchange risk and commodity price risk. We do not use derivative instruments for trading or speculative purposes. While the majority of our derivative instruments are designated as hedging instruments, we also enter into derivative instruments that are designed to hedge a risk, but are not designated as hedging instruments. These derivative instruments are adjusted to fair value through earnings at the end of each period. Our derivative and hedging programs are consistent with those described in the 2017 Form 10-K. The amount of ineffectiveness associated with these derivative instruments was immaterial for the three and six months ended December 31, 2017 and 2016.

During the six months ended December 31, 2017 and 2016, we entered into pay-floating interest rate swaps with a total notional amounts of $350 million and $100 million, respectively. These swaps have been designated as fair value hedges of our fixed rate debt and are included in other assets in the condensed consolidated balance sheet.

During the six months ended December 31, 2016, we entered into forward interest rate swaps with a total notional amount of $200 million to hedge probable, but not firmly committed, future transactions associated with our debt.

Fair Value of Financial Instruments

The carrying amounts of cash and equivalents, trade receivables, accounts payable and other accrued liabilities at December 31, 2017 and June 30, 2017 approximate fair value due to their short-term maturities.

The following table summarizes the estimated fair value of our long-term obligations and other short-term borrowings compared to the respective carrying amounts at:



(in millions)	December 31, 2017		June 30, 2017
Estimated fair value	$	9,801	$	10,713
Carrying amount	9,759		10,395

The fair value of our long-term obligations and other short-term borrowings is estimated based on either the quoted market prices for the same or similar issues or other inputs derived from available market information, which represents a Level 2 measurement.