	(in thousands)
December 31,	2019		2018
Industrial revenue bonds due from 2020 to 2040*	$	1,010,600	$	1,010,600
Notes, 4.125%, due 2022		600,000		600,000
Notes, 4.0%, due 2023		500,000		500,000
Notes, 3.95%, due 2028		500,000		500,000
Notes, 6.40%, due 2037		650,000		650,000
Notes, 5.20%, due 2043		500,000		500,000
Notes, 4.40%, due 2048		500,000		500,000
Finance lease obligations		85,224		—
Total long-term debt and finance lease obligations		4,345,824		4,260,600
Less debt issuance costs		25,259		27,324
Total amounts outstanding		4,320,565		4,233,276
Less current maturities of long-term debt		20,000		—
Less current portion of finance lease obligations		9,264		—
Total long-term debt and finance lease obligations due after one year	$	4,291,301	$	4,233,276

Annual aggregate long-term debt maturities are: $20.0 million in 2020, none in 2021, $601.0 million in 2022, $500.0 million in 2023, none in 2024 and $3.14 billion thereafter.

In April 2018, Nucor issued $500.0 million of 3.95% notes due 2028 and $500.0 million of 4.40% notes due 2048. Net proceeds of the issuances were $986.1 million, of which $500.0 million was used to repay the $500.0 million of 5.85% notes that matured June 1, 2018. Costs of $11.9 million associated with the issuances have been capitalized and will be amortized over the lives of the notes.

During the second quarter of 2018, Nucor amended its $1.50 billion unsecured revolving credit facility to extend the maturity date from April 2021 to April 2023. Costs associated with the amendment were immaterial. The unsecured revolving credit facility provides up to $1.50 billion in revolving loans and allows up to $500.0 million in additional commitments at Nucor’s election in accordance with the terms set forth in the credit agreement. Up to the equivalent of $850.0 million of the credit facility is available for foreign currency loans, up to $100.0 million is available for the issuance of letters of credit and up to $500.0 million is available for the issuance of revolving loans for Nucor subsidiaries in accordance with the terms set forth in the credit agreement. The credit facility provides for a pricing grid based upon the credit rating of Nucor’s senior unsecured long-term debt and, alternatively, interest rates quoted by lenders in connection with competitive bidding. The credit facility includes customary financial and other covenants, including a limit on the ratio of funded debt to total capital of 60%, a limit on Nucor’s ability to pledge the Company’s assets and a limit on consolidations, mergers and sales of assets. As of December 31, 2019, Nucor’s funded debt to total capital ratio was 29%, and Nucor was in compliance with all covenants under the credit facility. No borrowings were outstanding under the credit facility as of December 31, 2019 and 2018.

Harris Steel has credit facilities totaling approximately $19.0 million, with no outstanding borrowings at December 31, 2019 ($7.5 million at December 31, 2018). In addition, the business of Nucor Trading S.A. is financed by uncommitted trade credit arrangements with a number of European banking institutions. As of December 31, 2019, Nucor Trading S.A. had outstanding borrowings of $62.4 million, which is presented in short-term debt in the consolidated balance sheet ($57.9 million at December 31, 2018).

Letters of credit totaling $28.0 million were outstanding as of December 31, 2019 ($56.2 million as of December 31, 2018), related to certain obligations, including workers’ compensation, utilities deposits and credit arrangements by Nucor Trading S.A. for commitments to purchase inventories.