	March 31,		December 31,
	2020		2019
$1.1 billion in Senior Notes, interest at 3.95% payable semiannually, principal due on December 1, 2042	$	1,089	$	1,088
$0.5 billion in Senior Notes, interest at 3.60% payable semiannually, principal due on December 1, 2029		493		493
$0.4 billion in Senior Notes, interest at 2.60% payable semiannually, principal due on December 1, 2022		399		399
Other debt		21		9
Total	$	2,002	$	1,989

The Company has a $2.0 billion, five-year unsecured revolving credit facility, which expires on October 30, 2024. The Company has the right to increase the commitments under this agreement to an aggregate amount of up to $3.0 billion upon the consent of only those lenders holding any such increase. Interest under the 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 credit facility contains a financial covenant regarding maximum debt-to-capitalization ratio of 60%. As of March 31, 2020, the Company was in compliance with a debt-to-capitalization ratio of 29.2%.

Additionally, the Company has a $150 million bank line of credit for the construction of a facility in Saudi Arabia. Interest under the bank line of credit is based upon LIBOR plus 1.40%. The bank line of credit contains a financial covenant regarding maximum debt-to-equity ratio of 75%. As of March 31, 2020, the Company was in compliance.

The Company has a commercial paper program under which borrowings are classified as long-term since the program is supported by the $2.0 billion, five-year credit facility. At March 31, 2020, there were no commercial paper borrowings, and there were no outstanding letters of credit issued under the credit facility, resulting in $2.0 billion of funds available under this credit facility.

The Company had $524 million of outstanding letters of credit at March 31, 2020, primarily in the U.S. and Norway, that are under various bilateral letter of credit facilities. Letters of credit are issued as bid bonds, advanced payment bonds and performance bonds.

At March 31, 2020 and December 31, 2019, the fair value of the Company’s unsecured Senior Notes approximated $1,445 million and $1,947 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 March 31, 2020 and December 31, 2019, the carrying value of the Company’s unsecured Senior Notes approximated $1,981 million and $1,980 million, respectively.