

	Effective	March 31	December 31	March 31
in thousands	Interest Rates	2021	2020	2020
Short-term Debt
Bank line of credit expires 2025 ¹		$ 0	$ 0	$ 0
Total short-term debt		$ 0	$ 0	$ 0
Long-term Debt
Bank line of credit expires 2025 ¹		$ 0	$ 0	$ 0
Floating-rate notes due 2020		0	0	250,000
Floating-rate notes due 2021		0	500,000	500,000
8.85% notes due 2021	8.88%	6,000	6,000	6,000
4.50% notes due 2025	4.65%	400,000	400,000	400,000
3.90% notes due 2027	4.00%	400,000	400,000	400,000
3.50% notes due 2030	3.94%	750,000	750,000	0
7.15% notes due 2037	8.05%	129,239	129,239	129,239
4.50% notes due 2047	4.59%	700,000	700,000	700,000
4.70% notes due 2048	5.42%	460,949	460,949	460,949
Other notes	0.88%	11,277	11,711	179
Total long-term debt - face value		$ 2,857,465	$ 3,357,899	$ 2,846,367
Unamortized discounts and debt issuance costs		(69,128)	(70,224)	(60,776)
Total long-term debt - book value		$ 2,788,337	$ 3,287,675	$ 2,785,591
Less current maturities		15,436	515,435	25
Total long-term debt - reported value		$ 2,772,901	$ 2,772,240	$ 2,785,566
Estimated fair value of long-term debt		$ 3,219,828	$ 3,443,225	$ 2,926,140

Discounts and debt issuance costs are amortized using the effective interest method over the terms of the respective notes resulting in $1,096,000 and $1,258,000 of net interest expense for these items for the three months ended March 31, 2021 and 2020, respectively.

In September 2020, we executed a new five-year unsecured line of credit of $1,000,000,000, incurring $4,632,000 of transaction costs. The line of credit contains affirmative, negative and financial covenants customary for an unsecured investment-grade facility. There are two primary negative covenants: 1) a limit on our ability to incur secured debt, and 2) a maximum ratio of debt to EBITDA of 3.50:1 (upon certain acquisitions, the maximum ratio can be 3.75:1 for four quarters). As of March 31, 2021, we were in compliance with the line of credit covenants.

Borrowings on the line of credit bear interest, at our option, at either LIBOR plus a credit margin ranging from 1.125% to 1.875%, or Truist Bank’s base rate (generally, its prime rate) plus a credit margin ranging from 0.125% to 0.875%. The credit margin for both LIBOR and base rate borrowings is determined by our credit ratings. Standby letters of credit, which are issued under the line of credit and reduce availability, are charged a fee equal to the credit margin for LIBOR borrowings plus 0.175%. We also pay a commitment fee on the daily average unused amount of the line of credit that ranges from 0.125% to 0.275% determined by our credit ratings. As of March 31, 2021, the credit margin for LIBOR borrowings was 1.250%, the credit margin for base rate borrowings was 0.250%, and the commitment fee for the unused amount was 0.150%.

As of March 31, 2021, our available borrowing capacity under the line of credit was $943,665,000. Utilization of the borrowing capacity was as follows:

$56,335,000 was used to provide support for outstanding standby letters of credit

All of our $2,857,465,000 (face value) of term debt is unsecured. $2,846,188,000 of such debt is governed by three essentially identical indentures that contain customary investment-grade type covenants. The primary covenant in all three indentures limits the amount of secured debt we may incur without ratably securing such debt. As of March 31, 2021, we were in compliance with all term debt covenants.

In May 2020, we issued $750,000,000 of 3.50% senior notes due 2030. Total proceeds were $741,417,000 (net of discounts and transaction costs). $250,000,000 of the proceeds were used to retire the $250,000,000 floating rate notes due June 2020. The remainder of the proceeds, together with cash on hand, was used to retire the $500,000,000 floating rate notes due March 2021.

We provide, in the normal course of business, certain third-party beneficiaries with standby letters of credit to support our obligations to pay or perform according to the requirements of an underlying agreement. Such letters of credit typically have an initial term of one year, typically renew automatically, and can only be modified or canceled with the approval of the beneficiary. All of our standby letters of credit are issued by banks that participate in our $1,000,000,000 line of credit, and reduce the borrowing capacity thereunder. Our standby letters of credit as of March 31, 2021 are summarized by purpose in the table below: