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Intangible Assets (Tables)
 3 Months Ended
Mar. 31, 2024
Goodwill and Intangible Assets Disclosure [Abstract]  
Summary of Changes in Carrying Value
The following table represents our change in carrying value of intangible assets (in millions):
Gross Carrying AmountAccumulated AmortizationNet Carrying Amount
Three Months Ended March 31, 2024
Customer relationships, beginning of period$1,844.8 $(1,051.2)$793.6 
Amortization expense— (31.8)(31.8)
Customer relationships, end of period$1,844.8 $(1,083.0)$761.8 

Amortization expense was $31.8 million and $31.9 million for the three months ended March 31, 2024 and 2023, respectively.
Schedule of Amortization Expense
The following table summarizes our estimated aggregate amortization expense for the next five years and thereafter (in millions):

2024 (remaining)$95.8 
2025110.2 
2026106.3 
2027106.3 
2028106.3 
Thereafter236.9 
Total$761.8