Segments (Summary Of Segment Information) (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) segment	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Net income (loss)	$ (24.3)	$ 225.0	$ (47.7)	$ 239.1
Number of Operating Segments | segment			3
Depreciation, amortization and accretion	61.0	49.3	$ 117.1	89.1
Segment Reporting Information, Additional Information [Abstract]
Operating revenues	(352.7)	(683.4)	(1,080.6)	(1,518.6)
Costs of product/services sold	225.7	537.2	760.1	1,232.8
Operations and maintenance	31.6	34.7	69.2	63.3
General and administrative	29.5	22.3	44.4	59.5
Gain (loss) on long-lived assets	(3.8)	0.0	(4.8)	(2.0)
Goodwill impairment	0.0	0.0	(80.3)	0.0
Gain on acquisition	0.0	209.4	0.0	209.4
Earnings from unconsolidated affiliates, net	8.4	3.7	13.9	10.6
Other income, net	0.1	0.1	0.2	0.2
EBITDA	70.6	302.4	135.9	381.2
Goodwill	138.6		138.6		$ 218.9
Total assets	5,323.7		5,323.7		5,349.3
Marketing Supply and Logistics
Segment Reporting Information, Additional Information [Abstract]
Operating revenues				(1,123.9)
Crestwood Midstream Partners LP
Net income (loss)	(26.8)	222.9	(52.4)	234.5
Depreciation, amortization and accretion	64.6	52.7	124.2	96.1
Segment Reporting Information, Additional Information [Abstract]
Operating revenues	(352.7)	(683.4)	(1,080.6)	(1,518.6)
Costs of product/services sold	225.7	537.2	760.1	1,232.8
Operations and maintenance	31.6	34.7	69.2	63.3
General and administrative	28.4	20.9	41.9	56.9
Gain (loss) on long-lived assets	(3.8)	0.0	(4.8)	(2.0)
Goodwill impairment	0.0	0.0	(80.3)	0.0
Gain on acquisition	0.0	209.4	0.0	209.4
Earnings from unconsolidated affiliates, net	8.4	3.7	13.9	10.6
EBITDA	71.6	303.7	138.2	383.6
Goodwill	138.6		138.6		218.9
Total assets	5,472.3		5,472.3		$ 5,504.0
Intersegment Eliminations
Segment Reporting Information, Additional Information [Abstract]
Operating revenues	16.7	28.6	59.3	85.0
Intersegment Eliminations | Gathering and Processing Operations
Segment Reporting Information, Additional Information [Abstract]
Operating revenues	(14.3)	(25.4)	(54.3)	(78.2)
Intersegment Eliminations | Storage and Transportation
Segment Reporting Information, Additional Information [Abstract]
Operating revenues	(2.4)	(3.2)	(5.0)	(6.8)
Intersegment Eliminations | Marketing Supply and Logistics
Segment Reporting Information, Additional Information [Abstract]
Operating revenues	16.7	28.6	59.3	85.0
Intersegment Eliminations | Crestwood Midstream Partners LP | Gathering and Processing Operations
Segment Reporting Information, Additional Information [Abstract]
Operating revenues	(14.3)	(25.4)	(54.3)	(78.2)
Intersegment Eliminations | Crestwood Midstream Partners LP | Storage and Transportation
Segment Reporting Information, Additional Information [Abstract]
Operating revenues	(2.4)	(3.2)	(5.0)	(6.8)
Intersegment Eliminations | Crestwood Midstream Partners LP | Marketing Supply and Logistics
Segment Reporting Information, Additional Information [Abstract]
Operating revenues	16.7	28.6	59.3	85.0
Corporate and Eliminations [Member]
Segment Reporting Information, Additional Information [Abstract]
Operating revenues	0.0	0.0	0.0	0.0
Corporate and Eliminations [Member] | Crestwood Midstream Partners LP
Segment Reporting Information, Additional Information [Abstract]
Operating revenues	0.0	0.0	0.0	0.0
Operating Segments | Gathering and Processing Operations
Segment Reporting Information, Additional Information [Abstract]
Operating revenues	(114.5)	(199.7)	(329.4)	(382.0)
Costs of product/services sold	21.3	108.9	129.6	246.9
Operations and maintenance	19.3	24.6	46.3	42.7
General and administrative	0.0	0.0	0.0	0.0
Gain (loss) on long-lived assets	(3.6)	(0.2)	(4.6)	(2.0)
Goodwill impairment			(80.3)
Gain on acquisition		209.4		209.4
Earnings from unconsolidated affiliates, net	(1.0)	(2.8)	(0.2)	(3.0)
Other income, net	0.0	0.0	0.0	0.0
EBITDA	83.6	298.0	122.7	375.0
Goodwill	45.9		45.9
Total assets	3,589.8		3,589.8
Operating Segments | Storage and Transportation
Segment Reporting Information, Additional Information [Abstract]
Operating revenues	(3.1)	(4.9)	(6.6)	(12.7)
Costs of product/services sold	0.1	0.0	0.3	0.0
Operations and maintenance	0.7	0.9	2.1	1.9
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		0.0
Earnings from unconsolidated affiliates, net	9.4	6.5	14.1	13.6
Other income, net	0.0	0.0	0.0	0.0
EBITDA	14.1	13.7	23.3	31.2
Goodwill	0.0		0.0
Total assets	964.7		964.7
Operating Segments | Marketing Supply and Logistics
Segment Reporting Information, Additional Information [Abstract]
Operating revenues	(235.1)	(478.8)	(744.6)	(1,123.9)
Costs of product/services sold	204.3	428.3	630.2	985.9
Operations and maintenance	11.6	9.2	20.8	18.7
General and administrative	0.0	0.0	0.0	0.0
Gain (loss) on long-lived assets	(0.2)	0.0	(0.2)	(0.2)
Goodwill impairment			0.0
Gain on acquisition		0.0		0.0
Earnings from unconsolidated affiliates, net	0.0	0.0	0.0	0.0
Other income, net	0.0	0.0	0.0	0.0
EBITDA	2.3	12.7	34.1	34.1
Goodwill	92.7		92.7
Total assets	736.9		736.9
Operating Segments | Crestwood Midstream Partners LP | Gathering and Processing Operations
Segment Reporting Information, Additional Information [Abstract]
Operating revenues	(114.5)	(199.7)	(329.4)	(382.0)
Costs of product/services sold	21.3	108.9	129.6	246.9
Operations and maintenance	19.3	24.6	46.3	42.7
General and administrative	0.0	0.0	0.0	0.0
Gain (loss) on long-lived assets	(3.6)	(0.2)	(4.6)	(2.0)
Goodwill impairment			(80.3)
Gain on acquisition		209.4		209.4
Earnings from unconsolidated affiliates, net	(1.0)	(2.8)	(0.2)	(3.0)
EBITDA	83.6	298.0	122.7	375.0
Goodwill	45.9		45.9
Total assets	3,742.1		3,742.1
Operating Segments | Crestwood Midstream Partners LP | Storage and Transportation
Segment Reporting Information, Additional Information [Abstract]
Operating revenues	(3.1)	(4.9)	(6.6)	(12.7)
Costs of product/services sold	0.1	0.0	0.3	0.0
Operations and maintenance	0.7	0.9	2.1	1.9
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		0.0
Earnings from unconsolidated affiliates, net	9.4	6.5	14.1	13.6
EBITDA	14.1	13.7	23.3	31.2
Goodwill	0.0		0.0
Total assets	964.7		964.7
Operating Segments | Crestwood Midstream Partners LP | Marketing Supply and Logistics
Segment Reporting Information, Additional Information [Abstract]
Operating revenues	(235.1)	(478.8)	(744.6)	(1,123.9)
Costs of product/services sold	204.3	428.3	630.2	985.9
Operations and maintenance	11.6	9.2	20.8	18.7
General and administrative	0.0	0.0	0.0	0.0
Gain (loss) on long-lived assets	(0.2)	0.0	(0.2)	(0.2)
Goodwill impairment			0.0
Gain on acquisition		0.0		0.0
Earnings from unconsolidated affiliates, net	0.0	0.0	0.0	0.0
EBITDA	2.3	12.7	34.1	34.1
Goodwill	92.7		92.7
Total assets	736.9		736.9
Corporate, Non-Segment
Segment Reporting Information, Additional Information [Abstract]
Operating 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	29.5	22.3	44.4	59.5
Gain (loss) on long-lived assets	0.0	0.2	0.0	0.2
Goodwill impairment			0.0
Gain on acquisition		0.0		0.0
Earnings from unconsolidated affiliates, net	0.0	0.0	0.0	0.0
Other income, net	0.1	0.1	0.2	0.2
EBITDA	(29.4)	(22.0)	(44.2)	(59.1)
Goodwill	0.0		0.0
Total assets	32.3		32.3
Corporate, Non-Segment | Crestwood Midstream Partners LP
Segment Reporting Information, Additional Information [Abstract]
Operating 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	28.4	20.9	41.9	56.9
Gain (loss) on long-lived assets	0.0	0.2	0.0	0.2
Goodwill impairment			0.0
Gain on acquisition		0.0		0.0
Earnings from unconsolidated affiliates, net	0.0	0.0	0.0	0.0
EBITDA	(28.4)	$ (20.7)	(41.9)	$ (56.7)
Goodwill	0.0		0.0
Total assets	$ 28.6		$ 28.6