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Intangible Assets (Tables)
 12 Months Ended
Dec. 31, 2022
Goodwill and Intangible Assets Disclosure [Abstract]  
Schedule of finite-lived intangible assets There were no changes in the carrying amount of goodwill during the fiscal years ended December 31, 2022 and 2021, respectively.
December 31, 2022December 31, 2021
Weighted - Average Remaining Amortization YearsGross Carrying AmountAccumulated AmortizationNetGross Carrying AmountAccumulated AmortizationNet
(Dollars in millions)
Customer relationships26.7 5.6 1.1 6.7 5.0 1.7 
Permits2031.7 4.5 27.2 31.7 3.1 28.6 
Other281.6 0.1 1.5 1.6 0.1 1.5 
Total$40.0 $10.2 $29.8 $40.0 $8.2 $31.8 
Schedule of finite-lived intangible assets, future amortization expense Based on the carrying value of finite-lived intangible assets as of December 31, 2022, we estimate amortization expense for each of the next five years as follows:
(Dollars in millions)
2023$2.0 
20241.9 
20251.5 
20261.5 
20271.4 
Thereafter21.5 
Total$29.8