Segments (Summary Of Segment Information) (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) segment	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Net income (loss)	$ 4.6	$ 33.6	$ (43.1)	$ 272.7
Number of Operating Segments | segment			3
Depreciation, amortization and accretion	60.8	51.5	$ 177.9	140.6
Segment Reporting Information, Additional Information [Abstract]
Revenues	519.2	823.6	1,599.8	2,342.2
Costs of product/services sold	358.7	657.4	1,118.8	1,890.2
Operations and maintenance	31.0	36.0	100.2	99.3
General and administrative	19.6	24.9	64.0	84.4
Gain (loss) on long-lived assets	(21.3)	(0.1)	(26.1)	(2.1)
Goodwill impairment	0.0	0.0	(80.3)	0.0
Gain on acquisition	0.0	0.0	0.0	209.4
Earnings from unconsolidated affiliates, net	10.5	10.4	24.4	21.0
Other income, net		0.1	0.2	0.3
EBITDA	99.1	115.7	235.0	496.9
Goodwill	138.6		138.6		$ 218.9
Total assets	5,294.2		5,294.2		5,349.3
Marketing Supply and Logistics
Segment Reporting Information, Additional Information [Abstract]
Revenues				1,685.6
Crestwood Midstream Partners LP
Net income (loss)	2.3	31.2	(50.1)	265.7
Depreciation, amortization and accretion	64.2	55.1	188.4	151.2
Segment Reporting Information, Additional Information [Abstract]
Revenues	519.2	823.6	1,599.8	2,342.2
Costs of product/services sold	358.7	657.4	1,118.8	1,890.2
Operations and maintenance	31.0	36.0	100.2	99.3
General and administrative	18.5	23.7	60.4	80.6
Gain (loss) on long-lived assets	(21.3)	(0.1)	(26.1)	(2.1)
Goodwill impairment	0.0	0.0	(80.3)	0.0
Gain on acquisition	0.0	0.0	0.0	209.4
Earnings from unconsolidated affiliates, net	10.5	10.4	24.4	21.0
EBITDA	100.2	116.8	238.4	500.4
Goodwill	138.6		138.6		218.9
Total assets	5,438.8		5,438.8		$ 5,504.0
Intersegment Eliminations
Segment Reporting Information, Additional Information [Abstract]
Revenues	(46.8)	(37.1)	(106.1)	(122.1)
Intersegment Eliminations | Gathering and Processing Operations
Segment Reporting Information, Additional Information [Abstract]
Revenues	44.9	33.6	99.2	111.8
Intersegment Eliminations | Storage and Transportation
Segment Reporting Information, Additional Information [Abstract]
Revenues	1.9	3.5	6.9	10.3
Intersegment Eliminations | Marketing Supply and Logistics
Segment Reporting Information, Additional Information [Abstract]
Revenues	(46.8)	(37.1)	(106.1)	(122.1)
Intersegment Eliminations | Crestwood Midstream Partners LP | Gathering and Processing Operations
Segment Reporting Information, Additional Information [Abstract]
Revenues	44.9	33.6	99.2	111.8
Intersegment Eliminations | Crestwood Midstream Partners LP | Storage and Transportation
Segment Reporting Information, Additional Information [Abstract]
Revenues	1.9	3.5	6.9	10.3
Intersegment Eliminations | Crestwood Midstream Partners LP | Marketing Supply and Logistics
Segment Reporting Information, Additional Information [Abstract]
Revenues	(46.8)	(37.1)	(106.1)	(122.1)
Corporate and Eliminations [Member]
Segment Reporting Information, Additional Information [Abstract]
Revenues	0.0	0.0	0.0	0.0
Corporate and Eliminations [Member] | Crestwood Midstream Partners LP
Segment Reporting Information, Additional Information [Abstract]
Revenues	0.0	0.0	0.0	0.0
Operating Segments | Gathering and Processing Operations
Segment Reporting Information, Additional Information [Abstract]
Revenues	145.2	257.8	474.6	639.8
Costs of product/services sold	63.2	164.1	192.8	411.0
Operations and maintenance	19.4	27.5	65.7	70.2
General and administrative	0.0	0.0	0.0	0.0
Gain (loss) on long-lived assets	(19.1)	(0.1)	(23.7)	(2.1)
Goodwill impairment			(80.3)
Gain on acquisition				209.4
Earnings from unconsolidated affiliates, net	0.5	(0.5)	0.3	(3.5)
Other income, net		0.0	0.0	0.0
EBITDA	88.9	99.2	211.6	474.2
Goodwill	45.9		45.9
Total assets	3,544.2		3,544.2
Operating Segments | Storage and Transportation
Segment Reporting Information, Additional Information [Abstract]
Revenues	3.5	4.1	10.1	16.8
Costs of product/services sold	0.0	0.1	0.3	0.1
Operations and maintenance	0.7	1.1	2.8	3.0
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
Gain on acquisition				0.0
Earnings from unconsolidated affiliates, net	10.0	10.9	24.1	24.5
Other income, net		0.0	0.0	0.0
EBITDA	14.7	17.3	38.0	48.5
Goodwill	0.0		0.0
Total assets	955.1		955.1
Operating Segments | Marketing Supply and Logistics
Segment Reporting Information, Additional Information [Abstract]
Revenues	370.5	561.7	1,115.1	1,685.6
Costs of product/services sold	295.5	493.2	925.7	1,479.1
Operations and maintenance	10.9	7.4	31.7	26.1
General and administrative	0.0	0.0	0.0	0.0
Gain (loss) on long-lived assets	(2.4)	0.0	(2.6)	(0.2)
Goodwill impairment			0.0
Gain on acquisition				0.0
Earnings from unconsolidated affiliates, net	0.0	0.0	0.0	0.0
Other income, net		0.0	0.0	0.0
EBITDA	14.9	24.0	49.0	58.1
Goodwill	92.7		92.7
Total assets	766.9		766.9
Operating Segments | Crestwood Midstream Partners LP | Gathering and Processing Operations
Segment Reporting Information, Additional Information [Abstract]
Revenues	145.2	257.8	474.6	639.8
Costs of product/services sold	63.2	164.1	192.8	411.0
Operations and maintenance	19.4	27.5	65.7	70.2
General and administrative	0.0	0.0	0.0	0.0
Gain (loss) on long-lived assets	(19.1)	(0.1)	(23.7)	(2.1)
Goodwill impairment			(80.3)
Gain on acquisition				209.4
Earnings from unconsolidated affiliates, net	0.5	(0.5)	0.3	(3.5)
EBITDA	88.9	99.2	211.6	474.2
Goodwill	45.9		45.9
Total assets	3,692.9		3,692.9
Operating Segments | Crestwood Midstream Partners LP | Storage and Transportation
Segment Reporting Information, Additional Information [Abstract]
Revenues	3.5	4.1	10.1	16.8
Costs of product/services sold	0.0	0.1	0.3	0.1
Operations and maintenance	0.7	1.1	2.8	3.0
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
Gain on acquisition				0.0
Earnings from unconsolidated affiliates, net	10.0	10.9	24.1	24.5
EBITDA	14.7	17.3	38.0	48.5
Goodwill	0.0		0.0
Total assets	955.1		955.1
Operating Segments | Crestwood Midstream Partners LP | Marketing Supply and Logistics
Segment Reporting Information, Additional Information [Abstract]
Revenues	370.5	561.7	1,115.1	1,685.6
Costs of product/services sold	295.5	493.2	925.7	1,479.1
Operations and maintenance	10.9	7.4	31.7	26.1
General and administrative	0.0	0.0	0.0	0.0
Gain (loss) on long-lived assets	(2.4)	0.0	(2.6)	(0.2)
Goodwill impairment			0.0
Gain on acquisition				0.0
Earnings from unconsolidated affiliates, net	0.0	0.0	0.0	0.0
EBITDA	14.9	24.0	49.0	58.1
Goodwill	92.7		92.7
Total assets	766.9		766.9
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	19.6	24.9	64.0	84.4
Gain (loss) on long-lived assets	0.2	0.0	0.2	0.2
Goodwill impairment			0.0
Gain on acquisition				0.0
Earnings from unconsolidated affiliates, net	0.0	0.0	0.0	0.0
Other income, net		0.1	0.2	0.3
EBITDA	(19.4)	(24.8)	(63.6)	(83.9)
Goodwill	0.0		0.0
Total assets	28.0		28.0
Corporate, Non-Segment | Crestwood Midstream Partners LP
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	18.5	23.7	60.4	80.6
Gain (loss) on long-lived assets	0.2	0.0	0.2	0.2
Goodwill impairment			0.0
Gain on acquisition				0.0
Earnings from unconsolidated affiliates, net	0.0	0.0	0.0	0.0
EBITDA	(18.3)	$ (23.7)	(60.2)	$ (80.4)
Goodwill	0.0		0.0
Total assets	$ 23.9		$ 23.9