Partnership Units and Related Matters - Summary of Distributions Declared and/or Paid by the Partnership (Details) - Distributions Paid [Member] - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019
Distributions Made To Members Or Limited Partners [Abstract]
Distributions payable date	Feb. 11, 2022	Nov. 11, 2021	Aug. 12, 2021	May 12, 2021	Feb. 11, 2021	Nov. 13, 2020	Aug. 13, 2020	May 13, 2020	Feb. 13, 2020	Nov. 13, 2019	Aug. 13, 2019	Apr. 05, 2019
Total Distributions	$ 103.7	$ 45.6	$ 45.5	$ 47.0	$ 54.3	$ 51.7	$ 51.7	$ 53.1	$ 241.9	$ 242.1	$ 242.4	$ 437.8
Distributions to Targa Resources Corp.	$ 103.7	$ 45.6	$ 45.5	$ 47.0	$ 47.6	$ 48.9	$ 48.9	$ 50.3	$ 239.1	$ 239.3	$ 239.6	$ 435.0