Funding for Employee Benefit Plans Debt Maturities, Purchases, and Retirement of Debt Issuance of Debt Credit Facilities We made contributions of $68.2 million and £3.4 million to our U.S. and U.K. defined contribution plans, respectively, in 2019 and expect to make contributions of approximately $75 million and £4 million during 2020. We made a de minimis amount of contributions to our U.S. qualified defined benefit pension plan and no contribution to our U.K. defined benefit pension plan during 2019. We do not expect to make any contributions to either plan during 2020. We have met all minimum pension funding requirements set forth by the Employee Retirement Income Security Act. We have estimated our future funding requirements under the Pension Protection Act of 2006 and under applicable U.K. law and do not believe that any future funding requirements will cause a material adverse effect on our liquidity. See Note 9 of the "Notes to Consolidated Financial Statements" contained herein in Item 8 for further discussion of our employee benefit plans. There are no significant financial covenants associated with any of our outstanding debt obligations. We continually monitor our debt covenants to ensure we remain in compliance. We have not observed any current trends that would cause a breach of any debt covenants. Northwind Holdings made principal payments on its floating rate, senior secured non-recourse notes of $60.0 million in each of 2019, 2018, and 2017. During 2019 we purchased and retired (i) $22.8 million aggregate liquidation amount of our 7.405% capital securities due 2038; (ii) $30.3 million aggregate principal amount of our 7.190% medium-term notes due 2028; (iii) $30.0 million aggregate principal amount of our 7.250% senior notes due 2028; and (iv) $350.0 million aggregate principal amount of our 3.000% senior notes due 2021. In 2018, our $200.0 million 7.00% senior unsecured notes matured. In 2017, we purchased and retired the remaining $3.4 million of principal on our senior secured floating rate notes acquired through our purchase of Starmount. In September 2019, we issued $450.0 million of 4.500% senior notes due 2049. The notes are callable at or above par and rank equally in the right of payment with all of our other unsecured and unsubordinated debt. In June 2019, we issued $400.0 million of 4.000% senior notes due 2029. The notes are callable at or above par and rank equally in the right of payment with all of our other unsecured and unsubordinated debt. In 2018, we issued $300.0 million of 6.25% junior subordinated notes due 2058. The notes are redeemable at or above par on or after June 15, 2023 and rank equally in the right of payment with our other junior subordinated debt securities. In April 2019, we amended the terms of our existing five-year unsecured revolving credit facility, increasing it from $400.0 million to $500.0 million. The credit facility, which was previously set to expire in 2021, was extended through April 2024. Under the terms of the amended agreement, we may request that the credit facility be increased up to $700.0 million, up from the previous amount of $600.0 million. We also may request, on up to two occasions, that the lenders' commitment termination dates be extended by one year. The credit facility provides for the issuance of letters of credit subject to certain terms and limitations. At December 31, 2019, letters of credit totaling $0.6 million had been issued from the credit facility, but there were no borrowed amounts outstanding. Also in April 2019, we separately entered into a three-year, $100.0 million unsecured revolving credit facility with a different syndicate of lenders, which is set to expire in April 2022. Under the terms of the agreement, we may request that the credit facility be increased up to $140.0 million. We also may request that the lenders' commitment termination dates be extended by one year. The credit facility provides for the issuance of letters of credit subject to certain terms and limitations. At 84