9. Debt

Debt consists of (in millions):


	December 31,
	2016		2015
$500 million in Senior Notes, interest at 1.35% payable semiannually, principal due on December 1, 2017		499		498
$1.4 billion in Senior Notes, interest at 2.60% payable semiannually, principal due on December 1, 2022		1,391		1,389
$1.1 billion in Senior Notes, interest at 3.95% payable semiannually, principal due on December 1, 2042		1,087		1,087
Commercial paper		—		890
Capital Leases and other debt		237		45

Total debt		3,214		3,909
Less current portion		506		2

Long-term debt	$	2,708	$	3,907

Principal payments of debt and capital leases for years subsequent to 2016 are as follows (in millions):


2017	$	506
2018		3
2019		4
2020		5
2021		5
Thereafter		2,691

	$	3,214

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

On January 1, 2016, the Company adopted Accounting Standards Update No. 2015-03 “Simplifying the Presentation of Debt Issuance Costs.” This update requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. We have applied the change retrospectively for prior period balances of unamortized debt issuance costs, resulting in a $21 million reduction in other assets and long-term debt on our consolidated balance sheet as of December 31, 2015. The table above now presents our debt liability net of the related debt discount and debt issuance costs.

The Company has a $4.5 billion, five-year credit facility which expires September 28, 2018. The Company also has a commercial paper program under which borrowings are classified as long-term since the program is supported by the $4.5 billion, five-year unsecured revolving credit facility. At December 31, 2016, there were no commercial paper borrowings, and there were no outstanding letters of credit issued under the credit facility, resulting in $4,500 million of funds available under this revolving credit facility. Interest under this multicurrency facility is based upon LIBOR, NIBOR or EURIBOR 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 December 31, 2016, the Company was in compliance with a debt-to-capitalization ratio of 18.7%.

The Company had $1,196 million of outstanding letters of credit at December 31, 2016, 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, 2016 and 2015, the fair value of the Company’s unsecured Senior Notes approximated $2,669 million and $2,551 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, 2016 and 2015, the carrying value of the Company’s unsecured Senior Notes approximated $2,977 million and $2,974 million, respectively.