Debt

Debt consisted of the following (in millions):



	March 31, 2018		December 31, 2017
SHORT-TERM DEBT
Commercial paper notes, bearing a weighted-average interest rate of 2.8% and 2.4%, respectively⁽¹⁾	$	116	$	—
Senior secured hedged inventory facility, bearing a weighted-average interest rate of 2.9% and 2.6%, respectively⁽¹⁾	285		664
Senior unsecured revolving credit facility, bearing a weighted-average interest rate of 3.0% ⁽¹⁾	238		—
Other	135		73
Total short-term debt ⁽²⁾	774		737

LONG-TERM DEBT
Senior notes, net of unamortized discounts and debt issuance costs of $65 and $67, respectively ⁽³⁾	8,935		8,933
Commercial paper notes and senior secured hedged inventory facility borrowings ⁽³⁾	—		247
Senior unsecured revolving credit facility ⁽³⁾	112		—
Other	3		3
Total long-term debt	9,050		9,183
Total debt ⁽⁴⁾	$	9,824	$	9,920


⁽¹⁾	We classified these commercial paper notes and credit facility borrowings as short-term as of March 31, 2018 and December 31, 2017, as these notes and borrowings were primarily designated as working capital borrowings, were required to be repaid within one year and were primarily for hedged NGL and crude oil inventory and NYMEX and ICE margin deposits.


⁽²⁾	As of March 31, 2018 and December 31, 2017, balance includes borrowings of $217 million and $212 million, respectively, for cash margin deposits with NYMEX and ICE, which are associated with financial derivatives used for hedging purposes.


⁽³⁾	As of March 31, 2018 and December 31, 2017, we classified a portion of our commercial paper notes and credit facility borrowings as long-term based on our ability and intent to refinance such amounts on a long-term basis.

⁽⁴⁾

Our fixed-rate senior notes had a face value of approximately $9.0 billion at both March 31, 2018 and December 31, 2017. We estimated the aggregate fair value of these notes as of March 31, 2018 and December 31, 2017 to be approximately $8.8 billion and $9.1 billion, respectively. Our fixed-rate senior notes are traded among institutions, and these trades are routinely published by a reporting service. Our determination of fair value is based on reported trading activity near the end of the reporting period. We estimate that the carrying value of outstanding borrowings under our credit facilities and commercial paper program approximates fair value as interest rates reflect current market rates. The fair value estimates for our senior notes, credit facilities and commercial paper program are based upon observable market data and are classified in Level 2 of the fair value hierarchy.

Borrowings and Repayments

Total borrowings under our credit facilities and commercial paper program for the three months ended March 31, 2018 and 2017 were approximately $10.5 billion and $18.8 billion, respectively. Total repayments under our credit facilities and commercial paper program were approximately $10.7 billion and $19.2 billion for the three months ended March 31, 2018 and 2017, respectively. The variance in total gross borrowings and repayments is impacted by various business and financial factors including, but not limited to, the timing, average term and method of general partnership borrowing activities.

Letters of Credit

In connection with our supply and logistics activities, we provide certain suppliers with irrevocable standby letters of credit to secure our obligation for the purchase and transportation of crude oil, NGL and natural gas. Additionally, we issue letters of credit to support insurance programs, derivative transactions and construction activities. At March 31, 2018 and December 31, 2017, we had outstanding letters of credit of $102 million and $166 million, respectively.