Goodwill and Intangible Assets (Tables)

6 Months Ended

Jun. 30, 2020

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 Amount		Accumulated Amortization		Net Carrying Amount
Six Months Ended June 30, 2020
Customer relationships, beginning of period	$	1,795.8	$	(545.9)	$	1,249.9
Amortization expense	—		(61.8)		(61.8)
Retirements (1)	(1.6)		0.6		(1.0)
Customer relationships, end of period	$	1,794.2	$	(607.1)	$	1,187.1

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(1)Intangible assets retired as a result of the disposition of certain non-core assets.

Schedule of Amortization Expense

The following table summarizes our estimated aggregate amortization expense for the next five years and thereafter (in millions):

2020 (remaining)	$	61.7
2021	123.4
2022	123.4
2023	123.4
2024	123.4
Thereafter	631.8
Total	$	1,187.1