CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (UNAUDITED) - USD ($) $ in Millions	Total	Non-controlling Interests	Common Units Partners' Capital General Public	Common Units Partners' Capital BP Holdco	Subordinated Units Partners' Capital BP Holdco	General Partner
Beginning Balance at Dec. 31, 2018	$ 210.9	$ 141.0	$ 836.8	$ (61.7)	$ (705.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	40.7	3.5	16.9	1.6	18.5	$ 0.2
Distributions to unitholders	(31.6)		(14.4)	(1.4)	(15.8)
Distributions to non-controlling interests	(4.6)	(4.6)
Ending Balance at Mar. 31, 2019	215.4	139.9	839.3	(61.5)	(702.5)	0.2
Beginning Balance at Dec. 31, 2018	210.9	141.0	836.8	(61.7)	(705.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	82.8
Ending Balance at Jun. 30, 2019	218.6	138.7	841.3	(61.3)	(700.5)	0.4
Beginning Balance at Mar. 31, 2019	215.4	139.9	839.3	(61.5)	(702.5)	0.2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	42.1	4.8	16.9	1.6	18.4	0.4
Distributions to unitholders	(33.0)		(15.0)	(1.4)	(16.4)	(0.2)
Unit-based compensation	0.1		0.1
Distributions to non-controlling interests	(6.0)	(6.0)
Ending Balance at Jun. 30, 2019	218.6	138.7	841.3	(61.3)	(700.5)	0.4
Beginning Balance at Dec. 31, 2019	240.2	136.9	851.6	(60.3)	(689.2)	1.2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	47.5	5.8	18.5	1.8	20.2	1.2
Distributions to unitholders	(37.6)		(16.6)	(1.6)	(18.2)	(1.2)
Unit-based compensation	0.1		0.1
Distributions to non-controlling interests	(6.7)	(6.7)
Ending Balance at Mar. 31, 2020	243.5	136.0	853.6	(60.1)	(687.2)	1.2
Beginning Balance at Dec. 31, 2019	240.2	136.9	851.6	(60.3)	(689.2)	1.2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	92.9
Ending Balance at Jun. 30, 2020	245.8	135.3	855.0	(60.0)	(685.7)	1.2
Beginning Balance at Mar. 31, 2020	243.5	136.0	853.6	(60.1)	(687.2)	1.2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	45.4	4.8	18.0	1.7	19.7	1.2
Distributions to unitholders	(37.6)		(16.6)	(1.6)	(18.2)	(1.2)
Unit-based compensation	0.0		0.0
Distributions to non-controlling interests	(5.5)	(5.5)
Ending Balance at Jun. 30, 2020	$ 245.8	$ 135.3	$ 855.0	$ (60.0)	$ (685.7)	$ 1.2