CONSOLIDATED STATEMENTS OF CHANGES IN OWNERS' EQUITY - USD ($) shares in Thousands, $ in Millions	Total	Limited Partner Preferred [Member]	Limited Partners Common [Member]	General Partner Units [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Non-controlling Interests [Member]
Balance at Dec. 31, 2018	$ 8,546.1	$ 120.6	$ 6,227.2	$ 802.6	$ 124.9	$ 1,270.8
Balance (in units) at Dec. 31, 2018		5,000	275,168	5,629
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Contributions from Targa Resources Corp.	190.0	$ 0.0	$ 186.2	$ 3.8	0.0	0.0
Contributions from Targa Resources Corp. (in units)		0	0	0
Sale of ownership interests in subsidiaries	1,609.0	$ 0.0	$ (10.5)	$ (0.2)	0.0	1,619.7
Distributions to noncontrolling interests	(85.5)	0.0	0.0	0.0	0.0	(85.5)
Contributions from noncontrolling interests	403.5	0.0	0.0	0.0	0.0	403.5
Other comprehensive income (loss)	(15.0)	0.0	0.0	0.0	(15.0)	0.0
Net income (loss)	32.7	5.6	(39.8)	(0.8)	0.0	67.7
Distributions	(679.1)	(5.6)	(660.0)	(13.5)	0.0	0.0
Balance at Jun. 30, 2019	10,001.7	$ 120.6	$ 5,703.1	$ 791.9	109.9	3,276.2
Balance (in units) at Jun. 30, 2019		5,000	275,168	5,629
Balance at Mar. 31, 2019	8,403.9	$ 120.6	$ 5,961.0	$ 797.1	64.8	1,460.4
Balance (in units) at Mar. 31, 2019		5,000	275,168	5,629
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Contributions from Targa Resources Corp.	190.0	$ 0.0	$ 186.2	$ 3.8	0.0	0.0
Contributions from Targa Resources Corp. (in units)		0	0	0
Sale of ownership interests in subsidiaries	1,609.0	$ 0.0	$ (10.5)	$ (0.2)	0.0	1,619.7
Distributions to noncontrolling interests	(66.9)	0.0	0.0	0.0	0.0	(66.9)
Contributions from noncontrolling interests	206.7	0.0	0.0	0.0	0.0	206.7
Other comprehensive income (loss)	45.1	0.0	0.0	0.0	45.1	0.0
Net income (loss)	51.7	2.8	(7.3)	(0.1)	0.0	56.3
Distributions	(437.8)	(2.8)	(426.3)	(8.7)	0.0	0.0
Balance at Jun. 30, 2019	10,001.7	$ 120.6	$ 5,703.1	$ 791.9	109.9	3,276.2
Balance (in units) at Jun. 30, 2019		5,000	275,168	5,629
Balance at Dec. 31, 2019	9,445.3	$ 120.6	$ 5,022.7	$ 778.0	122.5	3,401.5
Balance (in units) at Dec. 31, 2019		5,000	275,168	5,629
Balance at Mar. 31, 2020	7,103.9	$ 120.6	$ 2,803.6	$ 732.6	221.5	3,225.6
Balance (in units) at Mar. 31, 2020		5,000	275,168	5,629
Balance at Dec. 31, 2019	9,445.3	$ 120.6	$ 5,022.7	$ 778.0	122.5	3,401.5
Balance (in units) at Dec. 31, 2019		5,000	275,168	5,629
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Contributions from Targa Resources Corp.	50.0	$ 0.0	$ 49.0	$ 1.0	0.0	0.0
Contributions from Targa Resources Corp. (in units)		0	0	0
Distributions to noncontrolling interests	(204.3)	$ 0.0	$ 0.0	$ 0.0	0.0	(204.3)
Contributions from noncontrolling interests	25.7	0.0	0.0	0.0	0.0	25.7
Other comprehensive income (loss)	(94.1)	0.0	0.0	0.0	(94.1)	0.0
Net income (loss)	(1,948.7)	5.6	(1,922.9)	(39.4)	0.0	8.0
Distributions	(295.0)	(5.6)	(283.6)	(5.8)	0.0	0.0
Balance at Jun. 30, 2020	6,978.9	$ 120.6	$ 2,865.2	$ 733.8	28.4	3,230.9
Balance (in units) at Jun. 30, 2020		5,000	275,168	5,629
Balance at Mar. 31, 2020	7,103.9	$ 120.6	$ 2,803.6	$ 732.6	221.5	3,225.6
Balance (in units) at Mar. 31, 2020		5,000	275,168	5,629
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Contributions from Targa Resources Corp.	50.0	$ 0.0	$ 49.0	$ 1.0	0.0	0.0
Contributions from Targa Resources Corp. (in units)		0	0	0
Distributions to noncontrolling interests	(103.1)	$ 0.0	$ 0.0	$ 0.0	0.0	(103.1)
Contributions from noncontrolling interests	15.1	0.0	0.0	0.0	0.0	15.1
Other comprehensive income (loss)	(193.1)	0.0	0.0	0.0	(193.1)	0.0
Net income (loss)	159.2	2.8	61.9	1.2	0.0	93.3
Distributions	(53.1)	(2.8)	(49.3)	(1.0)	0.0	0.0
Balance at Jun. 30, 2020	$ 6,978.9	$ 120.6	$ 2,865.2	$ 733.8	$ 28.4	$ 3,230.9
Balance (in units) at Jun. 30, 2020		5,000	275,168	5,629