The following table summarizes information relating to our long-term debt, which we collectively refer to as our Senior Notes (in millions, except interest rates):

	January 25, 2019						April 27, 2018
				Effective						Effective
	Amount			Interest Rate			Amount			Interest Rate
2.00% Senior Notes Due September 2019	$	400			2.32	%	$	400			2.32	%
3.375% Senior Notes Due June 2021		500			3.54	%		500			3.54	%
3.25% Senior Notes Due December 2022		250			3.43	%		250			3.43	%
3.30% Senior Notes Due September 2024		400			3.42	%		400			3.42	%
Total principal amount		1,550						1,550
Unamortized discount and issuance costs		(7	)					(9	)
Total senior notes		1,543						1,541
Less: Current portion of long-term debt		(399	)					—
Total long-term debt	$	1,144					$	1,541

Our 2.00% Senior Notes and 3.30% Senior Notes, each with a principal amount of $400 million, were issued in September 2017. Interest on these Senior Notes is paid semi-annually in March and September. Our 3.375% Senior Notes and 3.25% Senior Notes, with principal amounts of $500 million and $250 million, respectively, were issued in June 2014 and December 2012, respectively. Interest on these Senior Notes is paid semi-annually in June and December. Our Senior Notes, which are unsecured, unsubordinated obligations, rank equally in right of payment with any existing and future senior unsecured indebtedness.

We may redeem the Senior Notes in whole or in part, at any time at our option at specified redemption prices. In addition, upon the occurrence of certain change of control triggering events, we may be required to repurchase the Senior Notes under specified terms. The Senior Notes also include covenants that limit our ability to incur debt secured by liens on assets or on shares of stock or indebtedness of our subsidiaries; to engage in certain sale and lease-back transactions; and to consolidate, merge or sell all or substantially all of our assets. As of January 25, 2019, we were in compliance with all covenants associated with the Senior Notes.

As of January 25, 2019, our aggregate future principal debt maturities are as follows (in millions):

We have a commercial paper program (the Program), under which we may issue unsecured commercial paper notes. Amounts available under the Program, as amended in July 2017, may be borrowed, repaid and re-borrowed, with the aggregate face or principal amount of the notes outstanding under the Program at any time not to exceed $1.0 billion. The maturities of the notes can vary, but may not exceed 397 days from the date of issue. The notes are sold under customary terms in the commercial paper market and may be issued at a discount from par or, alternatively, may be sold at par and bear interest at rates dictated by market conditions at the time of their issuance. The proceeds from the issuance of the notes are used for general corporate purposes. As of January 25, 2019, we had commercial paper notes outstanding with an aggregate principal amount of $164 million, a weighted-average interest rate of 2.87% and maturities ranging from 27 days to 36 days. As of April 27, 2018, we had commercial paper notes outstanding with an aggregate principal amount of $385 million, a weighted-average interest rate of 2.29% and maturities ranging from 19 days to 32 days.

In connection with the Program, we have a senior unsecured credit agreement with a syndicated group of lenders that expires on December 10, 2021. The credit agreement, as amended in July 2017, provides a $1.0 billion revolving unsecured credit facility, with a $50 million letter of credit sub-facility, that serves as a back-up for the Program. Proceeds from the facility may also be used for general corporate purposes to the extent that the credit facility exceeds the outstanding debt issued under the Program. The credit agreement includes options that allow us to request an increase in the facility of up to an additional $300 million and to extend its maturity date for two additional one-year periods, both subject to certain conditions. As of January 25, 2019 we were in compliance with all associated covenants in this agreement. No amounts were drawn against this facility during any of the periods presented.