DEBT

The carrying value of long-term debt outstanding was as follows at December 31, 2017 and 2016:



	2017		2016
	(in millions)
Long-term debt:
Senior notes:
$500 million, 7.20% due June 15, 2018	$	—	$	501
$300 million, 6.30% due August 1, 2018	—		304
$400 million, 2.625% due October 1, 2019	399		398
$400 million, 2.50% due December 15, 2020	397		—
$400 million, 2.90% due December 15, 2022	396		—
$600 million, 3.15% due December 1, 2022	595		595
$600 million, 3.85% due October 1, 2024	595		595
$600 million, 3.95% due March 15, 2027	594		—
$250 million, 8.15% due June 15, 2038	263		264
$400 million, 4.625% due December 1, 2042	396		396
$750 million, 4.95% due October 1, 2044	739		739
$400 million, 4.80% due March 15, 2047	396		—
Total long-term debt	$	4,770	$	3,792

Senior Notes

In December 2017, we issued $400 million of 2.50% senior notes due December 15, 2020 and $400 million of 2.90% senior notes due December 15, 2022. Our net proceeds, reduced for the underwriters' discount and commission and offering expenses paid as of December 31, 2017, were $794 million. We used the net proceeds, together with available cash, to fund the redemption of our $300 million aggregate principal amount of 6.30% senior notes maturing in August 2018 and our $500 million aggregate principal amount of 7.20% senior notes maturing in June 2018 at 100% of the principal amount plus applicable premium for early redemption and accrued and unpaid interest to the redemption date, for cash totaling approximately $829 million. We recognized a loss on extinguishment of debt of approximately $17 million in December 2017 for the redemption of these senior notes, which is included in interest expense in the consolidated statements of income.

In March 2017, we issued $600 million of 3.95% senior notes due March 15, 2027 and $400 million of 4.80% senior notes due March 15, 2047. Our net proceeds, reduced for the underwriters' discount and commission and offering expenses paid as of March 31, 2017, were $991 million. The net proceeds from these issuances are being used for general corporate purposes.

Our senior notes, which are unsecured, may be redeemed at our option at any time at 100% of the principal amount plus accrued interest and a specified make-whole amount. The 8.15% senior notes are subject to an interest rate adjustment if the debt ratings assigned to the notes are downgraded (or subsequently upgraded). In addition, our senior notes contain a change of control provision that may require us to purchase the notes under certain circumstances.

Credit Agreement

In May 2017 we amended and restated our previous 5-year $1.0 billion unsecured revolving credit agreement expiring July 2018 with a 5-year $2.0 billion unsecured revolving credit agreement which expires May 2022. Under the credit agreement, at our option, we can borrow on either a competitive advance basis or a revolving credit basis. The revolving credit portion bears interest at either LIBOR plus a spread or the base rate plus a spread. The LIBOR spread, currently 110 basis points, varies depending on our credit ratings ranging from 91 to 150 basis points. We also pay an annual facility fee regardless of utilization. This facility fee, currently 15 basis points, may fluctuate between 9 and 25 basis points, depending upon our credit ratings. The competitive advance portion of any borrowings will bear interest at market rates prevailing at the time of borrowing on either a fixed rate or a floating rate based on LIBOR, at our option.

The terms of the credit agreement include standard provisions related to conditions of borrowing, including a customary material adverse effect clause which could limit our ability to borrow additional funds. In addition, the credit agreement contains customary restrictive and financial covenants as well as customary events of default, including financial covenants regarding the maintenance of a minimum level of net worth of $9.2 billion at December 31, 2017 and a maximum leverage ratio of 3.0:1. We are in compliance with the financial covenants, with actual net worth of $9.8 billion and an actual leverage ratio of 1.0:1, as measured in accordance with the credit agreement as of December 31, 2017. Upon our agreement with one or more financial institutions, we may expand the aggregate commitments under the credit agreement to a maximum of $2.5 billion, through a $500 million incremental loan facility.

At December 31, 2017, we had no borrowings outstanding under the credit agreement and no letters of credit outstanding under the credit agreement. Accordingly, as of December 31, 2017, we had $2 billion of remaining borrowing capacity (which excludes the uncommitted $500 million incremental loan facility under the credit agreement), none of which would be restricted by our financial covenant compliance requirement. We have other customary, arms-length relationships, including financial advisory and banking, with some parties to the credit agreement.

Commercial Paper

We previously entered into a commercial paper program pursuant to which we may issue short-term, unsecured commercial paper notes privately placed on a discount basis through certain broker dealers. On June 15, 2017, we increased the size of the commercial paper program to permit the issuance of the commercial notes with the aggregate face or principal amount outstanding under the program at any time not to exceed $2 billion. Amounts available under the program may be borrowed, repaid and re-borrowed from time to time. The net proceeds of issuances have been and are expected to be used for general corporate purposes. The maximum principal amount outstanding at any one time during the year ended December 31, 2017 was $500 million, with $150 million outstanding at December 31, 2017, compared to $300 million outstanding at December 31, 2016.