Debt

Total debt at March 31, 2018 and December 31, 2017 consisted of the following:



	Interest rate	March 31, 2018		December 31, 2017
Notes due March 2018	5.6%	$	—	$	250,000
Notes due March 2019	6.25%	300,000		300,000
Notes due September 2020	3.625%	300,000		300,000
Notes due October 2021	3.625%	600,000		600,000
Notes due May 2022	4.125%	400,000		400,000
Notes due April 2023	4.7%	400,000		400,000
Notes due March 2024	4.625%	500,000		500,000
Notes due January 2037	5.25%	35,841		35,841
Notes due March 2043	6.7%	425,000		425,000
Term loans	Variable	645,000		650,000
Other debt		5,432		5,476
Principal amount		3,611,273		3,866,317
Less: unamortized costs, net		35,131		35,982
Total debt		3,576,142		3,830,335
Less: current portion long-term debt		327,429		271,057
Long-term debt		$	3,248,713	$	3,559,278

During the first quarter of 2018, we repaid the $250 million of 5.6% Notes that matured in March 2018 and $5 million of principal related to our term loans.

On May 4, 2018, Standard & Poor’s lowered our corporate credit rating to BB+ from BBB-. Interest rates on certain notes and term loans are subject to adjustment based on changes in our credit ratings. As a result, the coupon rate on $1.7 billion principal amount of our notes will increase by 0.25% effective at the next interest payment date for each security. The rate on our $650 million term loans will also increase 0.25%, effective immediately.

Additionally, the fees on our $1 billion credit facility are also subject to adjustment based on our credit ratings. As a result of the lower rating, the undrawn fee on the credit facility will increase 0.05% and the fee on any drawn amounts will increase 0.20%. As of March 31, 2018, we have not drawn upon the credit facility.