Goodwill and Intangible Assets (Tables)

12 Months Ended

Dec. 31, 2020

Goodwill and Intangible Assets Disclosure [Abstract]

The tables below provide a summary of our change in carrying amount of goodwill by segment (in millions) for the years ended December 31, 2020, 2019, and 2018 by assigned reporting unit.


	Permian		Louisiana		Oklahoma		North Texas		Corporate		Totals
Year Ended December 31, 2020
Balance, beginning of period	$	184.6	$	—	$	—	$	—	$	—	$	184.6
Impairment	(184.6)		—		—		—		—		(184.6)
Balance, end of period	$	—	$	—	$	—	$	—	$	—	$	—


	Permian		Louisiana		Oklahoma		North Texas		Corporate		Totals
Year Ended December 31, 2019
Balance, beginning of period	$	—	$	—	$	190.3	$	—	$	1,119.9	$	1,310.2
Goodwill allocation	184.6		186.5		623.1		125.7		(1,119.9)		—
Impairment	—		(186.5)		(813.4)		(125.7)		—		(1,125.6)
Balance, end of period	$	184.6	$	—	$	—	$	—	$	—	$	184.6


	Permian		Louisiana		Oklahoma		North Texas		Corporate		Totals
Year Ended December 31, 2018
Balance, beginning of period	$	29.3	$	—	$	190.3	$	202.7	$	1,119.9	$	1,542.2
Impairment	(29.3)		—		—		(202.7)		—		(232.0)
Balance, end of period	$	—	$	—	$	190.3	$	—	$	1,119.9	$	1,310.2

Summary of Changes in Carrying Value

The following table represents our change in carrying value of intangible assets for the periods stated (in millions):


	Gross Carrying Amount		Accumulated Amortization		Net Carrying Amount
Year Ended December 31, 2020
Customer relationships, beginning of period	$	1,795.8	$	(545.9)	$	1,249.9
Amortization expense	—		(123.5)		(123.5)
Retirements (1)	(1.6)		0.6		(1.0)
Customer relationships, end of period	$	1,794.2	$	(668.8)	$	1,125.4

Year Ended December 31, 2019
Customer relationships, beginning of period	$	1,795.8	$	(422.2)	$	1,373.6
Amortization expense	—		(123.7)		(123.7)
Customer relationships, end of period	$	1,795.8	$	(545.9)	$	1,249.9

Year Ended December 31, 2018
Customer relationships, beginning of period	$	1,795.8	$	(298.7)	$	1,497.1
Amortization expense	—		(123.5)		(123.5)
Customer relationships, end of period	$	1,795.8	$	(422.2)	$	1,373.6

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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):


2021	$	123.4
2022	123.4
2023	123.4
2024	123.4
2025	106.1
Thereafter	525.7
Total	$	1,125.4