Related Party Transactions - Targa - Summary of Transactions with Affiliates (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Summary of transactions with Targa [Abstract]
Cash distributions to Targa based on general partner and limited partner ownership		$ 53.1	$ 437.8	$ 295.0	$ 679.1
Cash contributions from Targa related to limited partner ownership				49.0	186.2
Targa Resources Corp. [Member]
Summary of transactions with Targa [Abstract]
Targa billings of payroll and related costs included in operating expenses		66.6	61.6	132.2	115.7
Targa allocation of general and administrative expense		56.0	61.1	108.5	128.8
Cash distributions to Targa based on general partner and limited partner ownership		50.3	435.0	289.4	673.5
Cash contributions from Targa related to limited partner ownership	[1]	49.0	186.2	49.0	186.2
Contributions from Targa Resources Corp		$ 1.0	$ 3.8	$ 1.0	$ 3.8
Targa Resources Corp. [Member] | Targa Resources GP LLC [Member]
Summary of transactions with Targa [Abstract]
Percentage of general partner's interest maintained		2.00%	2.00%	2.00%	2.00%

[1] The cash contributions from Targa related to limited partner ownership were allocated 98% to the limited partner and 2% to general partner. See Note 7 – Partnership Units and Related Matters.