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Debt and Letters of Credit
 3 Months Ended
Mar. 31, 2024
Debt Disclosure [Abstract]  
Debt and Letters of Credit Debt and Letters of Credit
Debt consisted of the following:
(in millions)March 31, 2024December 31, 2023
Borrowings under credit facility$— $— 
Senior Notes
2028 Notes (4.250% Senior Notes)
590 600 
Unamortized discount and deferred financing costs(3)(3)
2029 Notes (1.125% Convertible Senior Notes)
575 575 
Unamortized deferred financing costs(13)(14)
Total debt$1,149 $1,158 

Credit Facility
As of March 31, 2024, letters of credit totaling $450 million were outstanding under our $1.8 billion credit facility, which matures in February 2026. This credit facility contains customary financial covenants, including a debt-to-capitalization ratio that cannot exceed 0.60 to 1.00, a limitation on the aggregate amount of debt of the greater of $750 million or €750 million for our subsidiaries, and a minimum liquidity threshold of $1.2 billion, defined in the amended credit facility, which may be reduced to $1.0 billion upon the repayment of debt. The credit facility also contains provisions that will require us to provide collateral to secure the facility should we be downgraded to BB by S&P and Ba2 by Moody's, such collateral consisting broadly of our U.S. assets. Borrowings under the facility, which may be denominated in USD, EUR, GBP or CAD, bear interest at a base rate, plus an applicable borrowing margin. As of March 31, 2024, we had not made any borrowings under our credit facility line and maintained a borrowing capacity of $776 million.
Uncommitted Lines of Credit
As of March 31, 2024, letters of credit totaling $916 million were outstanding under uncommitted lines of credit.
Redemption of 2028 Notes
During the 2024 Quarter, we redeemed $10 million of aggregate outstanding 2028 Notes, with an immaterial earnings impact.