Fair Value Measurements

Assets and liabilities measured and recorded at fair value on a recurring basis consisted of the following (in millions):



	December 31, 2018						December 31, 2017
	Total		Level 1		Level 2		Total		Level 1		Level 2
Assets
Mutual funds	$	978	$	978	$	—	$	917	$	917	$	—
U.S. Government securities	105		—		105		116		—		116
Other securities	144		28		116		209		39		170
Derivatives	22		—		22		23		—		23
Liabilities
Derivatives	61		—		61		106		—		106
Assets measured at NAV
Other commingled funds	18						19

Substantially all assets measured at fair value, other than derivatives, represent investments held in a separate trust to fund certain of our non-qualified deferred compensation plans and are recorded in other noncurrent assets on our consolidated balance sheets. The fair values of mutual funds and certain other securities are determined by reference to the quoted market price per unit in active markets multiplied by the number of units held without consideration of transaction costs. The fair values of U.S. Government and other securities are determined using pricing models that use observable inputs (e.g., interest rates and yield curves observable at commonly quoted intervals), bids provided by brokers or dealers or quoted prices of securities with similar characteristics. The fair values of derivative instruments, which consist of foreign currency exchange forward and interest rate swap contracts, primarily are determined based on the present value of future cash flows using model-derived valuations that use observable inputs such as interest rates, credit spreads and foreign currency exchange rates.

In addition to the financial instruments listed in the table above, we hold other financial instruments, including cash and cash equivalents, receivables, accounts payable and debt and commercial paper. The carrying amounts for cash and cash equivalents, receivables and accounts payable approximated their fair values. The estimated fair value of our outstanding debt and commercial paper was $15.4 billion and $16.8 billion at December 31, 2018 and 2017. The outstanding principal amount was $15.3 billion and $15.5 billion at December 31, 2018 and 2017, excluding $1.2 billion of unamortized discounts and issuance costs. The estimated fair values of our outstanding debt were determined based on quoted prices for similar instruments in active markets (Level 2).