Segments (Summary Of Segment Information) (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) segment	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Net income (loss)	$ (39.6)	$ 4.6	$ (116.0)	$ (43.1)
Number of Operating Segments | segment			3
Depreciation, amortization and accretion	64.6	60.8	$ 182.6	177.9
Segment Reporting Information, Additional Information [Abstract]
Revenues	1,226.3	519.2	3,188.6	1,599.8
Costs of product/services sold	1,099.3	358.7	2,710.3	1,118.8
Operations and maintenance	31.6	31.0	90.2	100.2
General and administrative	25.9	19.6	67.4	64.0
Gain (loss) on long-lived assets	(18.5)	(21.3)	(19.6)	(26.1)
Goodwill impairment	0.0	0.0	0.0	(80.3)
Earnings (loss) from unconsolidated affiliates, net	4.9	10.5	(125.9)	24.4
Other income, net	0.1	0.0	0.2	0.2
EBITDA	56.0	99.1	175.4	235.0
Assets	4,574.5		4,574.5		$ 5,243.7
Corporate, Non-Segment
Segment Reporting Information, Additional Information [Abstract]
Assets	20.7		20.7		29.5
Intersegment Eliminations
Segment Reporting Information, Additional Information [Abstract]
Revenues	(127.9)	(46.8)	(322.9)	(106.1)
Gathering and Processing Segment | Operating Segments
Segment Reporting Information, Additional Information [Abstract]
Revenues	296.8	190.1	814.0	573.8
Assets	3,357.4		3,357.4		3,464.6
Storage and Transportation | Operating Segments
Segment Reporting Information, Additional Information [Abstract]
Revenues	4.3	5.4	13.8	17.0
Assets	163.6		163.6		944.6
Marketing Supply and Logistics | Operating Segments
Segment Reporting Information, Additional Information [Abstract]
Revenues	1,053.1	370.5	2,683.7	1,115.1
Marketing Supply and Logistics | Operating Segments
Segment Reporting Information, Additional Information [Abstract]
Assets	1,032.8		1,032.8		805.0
Crestwood Midstream Partners LP
Net income (loss)	(41.8)	2.3	(120.7)	(50.1)
Depreciation, amortization and accretion	68.2	64.2	193.2	188.4
Segment Reporting Information, Additional Information [Abstract]
Revenues	1,226.3	519.2	3,188.6	1,599.8
Costs of product/services sold	1,099.3	358.7	2,710.3	1,118.8
Operations and maintenance	31.6	31.0	90.2	100.2
General and administrative	24.4	18.5	61.3	60.4
Gain (loss) on long-lived assets	(18.5)	(21.3)	(19.6)	(26.1)
Goodwill impairment	0.0	0.0	0.0	(80.3)
Earnings (loss) from unconsolidated affiliates, net	4.9	10.5	(125.9)	24.4
EBITDA	57.4	100.2	181.3	238.4
Assets	4,705.6		4,705.6		5,385.5
Crestwood Midstream Partners LP | Corporate, Non-Segment
Segment Reporting Information, Additional Information [Abstract]
Revenues	0.0	0.0	0.0	0.0
Costs of product/services sold	0.0	0.0	0.0	0.0
Operations and maintenance	0.0	0.0	0.0	0.0
General and administrative	24.4	18.5	61.3	60.4
Gain (loss) on long-lived assets	0.0	0.2	0.0	0.2
Goodwill impairment				0.0
Earnings (loss) from unconsolidated affiliates, net	0.0	0.0	0.0	0.0
EBITDA	(24.4)	(18.3)	(61.3)	(60.2)
Assets	17.3		17.3		26.2
Crestwood Midstream Partners LP | Corporate and Eliminations [Member]
Segment Reporting Information, Additional Information [Abstract]
Revenues	0.0	0.0	0.0	0.0
Crestwood Midstream Partners LP | Gathering and Processing Segment | Operating Segments
Segment Reporting Information, Additional Information [Abstract]
Revenues	171.2	145.2	498.9	474.6
Costs of product/services sold	150.1	63.2	387.2	192.8
Operations and maintenance	19.5	19.4	55.6	65.7
General and administrative	0.0	0.0	0.0	0.0
Gain (loss) on long-lived assets	(18.5)	(19.1)	(19.7)	(23.7)
Goodwill impairment				(80.3)
Earnings (loss) from unconsolidated affiliates, net	4.2	0.5	4.4	0.3
EBITDA	112.9	88.9	355.9	211.6
Assets	3,491.9		3,491.9		3,609.7
Crestwood Midstream Partners LP | Gathering and Processing Segment | Intersegment Eliminations
Segment Reporting Information, Additional Information [Abstract]
Revenues	125.6	44.9	315.1	99.2
Crestwood Midstream Partners LP | Storage and Transportation | Operating Segments
Segment Reporting Information, Additional Information [Abstract]
Revenues	2.0	3.5	6.0	10.1
Costs of product/services sold	(0.2)	0.0	(0.2)	0.3
Operations and maintenance	1.5	0.7	3.1	2.8
General and administrative	0.0	0.0	0.0	0.0
Gain (loss) on long-lived assets	0.0	0.0	0.0	0.0
Goodwill impairment				0.0
Earnings (loss) from unconsolidated affiliates, net	0.7	10.0	(130.3)	24.1
EBITDA	3.7	14.7	(119.4)	38.0
Assets	163.6		163.6		944.6
Crestwood Midstream Partners LP | Storage and Transportation | Intersegment Eliminations
Segment Reporting Information, Additional Information [Abstract]
Revenues	2.3	1.9	7.8	6.9
Crestwood Midstream Partners LP | Marketing Supply and Logistics | Operating Segments
Segment Reporting Information, Additional Information [Abstract]
Revenues	1,053.1	370.5	2,683.7	1,115.1
Costs of product/services sold	949.4	295.5	2,323.3	925.7
Operations and maintenance	10.6	10.9	31.5	31.7
General and administrative	0.0	0.0	0.0	0.0
Gain (loss) on long-lived assets	0.0	(2.4)	0.1	(2.6)
Earnings (loss) from unconsolidated affiliates, net	0.0	0.0	0.0	0.0
EBITDA	(34.8)	14.9	6.1	49.0
Assets	1,032.8		1,032.8		$ 805.0
Crestwood Midstream Partners LP | Marketing Supply and Logistics | Intersegment Eliminations
Segment Reporting Information, Additional Information [Abstract]
Revenues	(127.9)	(46.8)	(322.9)	(106.1)
Crestwood Midstream Partners LP | Marketing Supply and Logistics | Operating Segments
Segment Reporting Information, Additional Information [Abstract]
Goodwill impairment				0.0
Crestwood Equity Partners LP
Segment Reporting Information, Additional Information [Abstract]
General and administrative	1.5	1.1	6.1	3.6
Other income, net	0.1		0.2	0.2
EBITDA	56.0	99.1	175.4	235.0
Crestwood Equity Partners LP | Corporate, Non-Segment
Segment Reporting Information, Additional Information [Abstract]
General and administrative	1.5	1.1	6.1	3.6
Other income, net	0.1		0.2	0.2
EBITDA	(25.8)	(19.4)	(67.2)	(63.6)
Crestwood Equity Partners LP | Gathering and Processing Segment | Operating Segments
Segment Reporting Information, Additional Information [Abstract]
General and administrative	0.0	0.0	0.0	0.0
Other income, net	0.0		0.0	0.0
EBITDA	112.9	88.9	355.9	211.6
Crestwood Equity Partners LP | Storage And Transportation Operations | Operating Segments
Segment Reporting Information, Additional Information [Abstract]
General and administrative	0.0	0.0	0.0	0.0
Other income, net	0.0		0.0	0.0
EBITDA	3.7	14.7	(119.4)	38.0
Crestwood Equity Partners LP | Marketing Supply and Logistics | Operating Segments
Segment Reporting Information, Additional Information [Abstract]
General and administrative	0.0	0.0	0.0	0.0
Other income, net	0.0		0.0	0.0
EBITDA	$ (34.8)	$ 14.9	$ 6.1	$ 49.0