Note 8 - Debt

Our debt consisted of the following at December 31, 2015 and 2014:

	December 31,			December 31,
	2015			2014
Senior unsecured notes:
3.45% Senior Notes due 2015	$	—		$	350,000
3.05% Senior Notes due 2016		299,997			299,982
2.50% Senior Notes due 2017		299,956			299,920
4.00% Senior Notes due 2018		249,602			—
7.50% Senior Notes due 2019		201,695			201,695
4.90% Senior Notes due 2020		499,287			499,151
4.625% Senior Notes due 2021		399,680			399,627
3.95% Senior Notes due 2022		399,354			399,264
5.95% Senior Notes due 2025		448,814			—
6.20% Senior Notes due 2040		399,896			399,895
6.05% Senior Notes due 2041		397,719			397,681
5.25% Senior Notes due 2042		498,338			498,310
6.95% Senior Notes due 2045		394,563			—
Total senior unsecured notes		4,488,901			3,745,525
Credit facilities & commercial paper program		—			1,123,495
Total debt		4,488,901			4,869,020
Less: Current maturities of long-term debt		(299,997	)		—
Total long-term debt	$	4,188,904		$	4,869,020

Credit Facilities and Commercial Paper Program

At December 31, 2015, we had two credit facilities with an aggregate maximum capacity of $2.7 billion, which are comprised of a five year $2.4 billion senior unsecured credit facility that matures in January 2020 and a $225 million 364-day senior unsecured credit facility that matured in January 2016 and was not renewed (together, the “Credit Facilities”).

We have a commercial paper program that allows us to issue up to $2.4 billion in unsecured commercial paper notes. Amounts issued under the commercial paper program are supported by the unused capacity under our Credit Facilities and, therefore, are classified as long-term on our Consolidated Balance Sheet. The outstanding amounts of commercial paper reduce availability under our Credit Facilities.

The $2.4 billion facility provides us with the ability to issue up to $500 million in letters of credit. The issuance of letters of credit under the facility reduces the amount available for borrowing. At December 31, 2015, we had no letters of credit issued under the facility.

Senior Unsecured Notes

In March 2015, we issued $1.1 billion aggregate principal amount of Senior Notes, which we issued through our indirect wholly-owned subsidiary, Noble Holding International Limited (“NHIL”). These Senior Notes were issued in three separate tranches, consisting of $250 million of 4.00% Senior Notes due 2018, $450 million of 5.95% Senior Notes due 2025 and $400 million of 6.95% Senior Notes due 2045. The weighted average coupon of all three tranches is 5.87%. The interest rate on these Senior Notes may be increased if the credit rating applicable to the notes is downgraded below investment grade (up to a maximum of 200 basis points). The net proceeds of approximately $1.08 billion, after expenses, were used to repay indebtedness outstanding under our Credit Facilities and commercial paper program.

In August 2015, we repaid our $350 million 3.45% Senior Notes using cash on hand.

Our $300 million 3.05% Senior Notes mature during the first quarter of 2016. We anticipate using cash on hand to repay the outstanding balances.

Covenants

The Credit Facilities and commercial paper program are guaranteed by our indirect, wholly-owned subsidiaries, NHIL and Noble Holding Corporation (“NHC”). The covenants and events of default under the two Credit Facilities are substantially similar, and each facility contains a covenant that limits our ratio of debt to total tangible capitalization, as defined in the Credit Facilities, to 0.60. At December 31, 2015, our ratio of debt to total tangible capitalization was approximately 0.38. We were in compliance with all covenants under the credit facilities as of December 31, 2015.

In addition to the covenants from the Credit Facilities noted above, the indentures governing our outstanding senior unsecured notes contain covenants that place restrictions on certain merger and consolidation transactions, unless we are the surviving entity or the other party assumes the obligations under the indenture, and on the ability to sell or transfer all or substantially all of our assets. In addition, there are restrictions on incurring or assuming certain liens and on entering into sale and lease-back transactions. At December 31, 2015, we were in compliance with all of our debt covenants.

Other

At December 31, 2015, we had letters of credit of $5 million, including bonds covering the temporary importation of equipment, performance bonds and expatriate visa guarantees.

Aggregate principal repayments of total debt for the next five years and thereafter are as follows:

2016				2017				2018				2019				2020				Thereafter				Total
$	299,997			$	299,956			$	249,602			$	201,695			$	499,287			$	2,938,364			$	4,488,901

Fair Value of Financial Instruments

Fair value represents the amount at which an instrument could be exchanged in a current transaction between willing parties. The estimated fair value of our senior notes was based on the quoted market prices for similar issues or on the current rates offered to us for debt of similar remaining maturities (Level 2 measurement). All remaining fair value disclosures are presented in Note 15 and Note 17.

The following table presents the estimated fair value of our total debt as of December 31, 2015 and 2014:

	December 31, 2015				December 31, 2014
	Carrying		Estimated		Carrying		Estimated
	Value		Fair Value		Value		Fair Value
Senior unsecured notes:
3.45% Senior Notes due 2015	$	—	$	—	$	350,000	$	354,992
3.05% Senior Notes due 2016		299,997		299,340		299,982		302,515
2.50% Senior Notes due 2017		299,956		284,334		299,920		287,014
4.00% Senior Notes due 2018		249,602		227,285		—		—
7.50% Senior Notes due 2019		201,695		194,273		201,695		212,068
4.90% Senior Notes due 2020		499,287		378,761		499,151		471,095
4.625% Senior Notes due 2021		399,680		289,450		399,627		363,837
3.95% Senior Notes due 2022		399,354		265,643		399,264		346,425
5.95% Senior Notes due 2025		448,814		308,870		—		—
6.20% Senior Notes due 2040		399,896		237,005		399,895		350,351
6.05% Senior Notes due 2041		397,719		239,464		397,681		343,653
5.25% Senior Notes due 2042		498,338		279,919		498,310		385,181
6.95% Senior Notes due 2045		394,563		255,887		—		—
Total senior unsecured notes		4,488,901		3,260,231		3,745,525		3,417,131
Credit facilities and commercial paper program		—		—		1,123,495		1,123,496
Total debt	$	4,488,901	$	3,260,231	$	4,869,020	$	4,540,627