9. Debt

Debt consists of (in millions):


	December 31,
	2017		2016
$500 million in Senior Notes, interest at 1.35% payable semiannually, principal due on December 1, 2017		—		499

$1.4 billion in Senior Notes, interest at 2.60% payable semiannually, principal due on December 1, 2022		1,392		1,391

$1.1 billion in Senior Notes, interest at 3.95% payable semiannually, principal due on December 1, 2042		1,088		1,087

Capital Leases and other debt		232		237

Total debt		2,712		3,214
Less current portion		6		506

Long-term debt	$	2,706	$	2,708

Principal payments of debt and capital leases for years subsequent to 2017 are as follows (in millions):


2018	$	6
2019		5
2020		5
2021		5
2022		1,405
Thereafter		1,286

	$	2,712

See Note 12 for additional details on future lease payments specific to capital leases.

On June 27, 2017, the Company entered into a new $3.0 billion credit agreement evidencing a five-year unsecured revolving credit facility, which expires on June 27, 2022, with a syndicate of financial institutions. This new credit facility replaced the Company’s previous $4.5 billion revolving credit facility. The Company has the right to increase the aggregate commitments under this new agreement to an aggregate amount of up to $4.0 billion upon the consent of only those lenders holding any such increase. Interest under the new multicurrency facility is based upon LIBOR, NIBOR or CDOR plus 1.125% subject to a ratings-based grid or the U.S. prime rate. The new credit facility contains a financial covenant regarding maximum debt-to-capitalization ratio of 60%. As of December 31, 2017, the Company was in compliance with a debt-to-capitalization ratio of 16.1%.

On November 29, 2017, the Company repaid in its entirety the $500 million of its 1.35% unsecured Senior Notes using available cash balances.

The Company has a commercial paper program under which borrowings are classified as long-term since the program is supported by the $3.0 billion, five-year credit facility. At December 31, 2017, there were no commercial paper borrowings, and there were no outstanding letters of credit issued under the credit facility, resulting in $3.0 billion of funds available under this credit facility.

The Company had $658 million of outstanding letters of credit at December 31, 2017, primarily in the U.S. and Norway, that are under various bilateral committed letter of credit facilities. Letters of credit are issued as bid bonds, advanced payment bonds and performance bonds.

At December 31, 2017 and 2016, the fair value of the Company’s unsecured Senior Notes approximated $2,346 million and $2,669 million, respectively. The fair value of the Company’s debt is estimated using Level 2 inputs in the fair value hierarchy and is based on quoted prices for those or similar instruments. At December 31, 2017 and 2016, the carrying value of the Company’s unsecured Senior Notes approximated $2,480 million and $2,977 million, respectively.