Condensed Consolidating Financial Information (Balance Sheet) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash	$ 14.5	$ 25.7
Accounts receivable	222.2	242.2
Inventory	100.1	53.7
Total current assets	396.3	376.4
Property, plant and equipment, net	2,951.7	2,909.1
Operating lease, right-of-use assets, net	39.6	53.8
Investment	953.0	980.4
Other non-current assets	5.4	5.5
Total assets	5,294.2	5,349.3
Current liabilities:
Accounts payable	141.1	189.2
Total current liabilities	337.2	357.8
Long-term liabilities:
Long-term debt, less current portion	2,548.9	2,328.3
Other long-term liabilities	289.1	301.6
Deferred income taxes	2.2	2.6
Total liabilities	3,177.4	2,990.3
Interest of non-controlling partner in subsidiary	431.6	426.2	$ 425.1	$ 0.0
Total partners’ capital	1,685.2	1,932.8
Total liabilities and capital	5,294.2	5,349.3
Eliminations
Current assets:
Cash	0.0	0.0
Accounts receivable	0.0	0.0
Inventory	0.0	0.0
Other	0.0	0.0
Total current assets	0.0	0.0
Property, plant and equipment, net	0.0	0.0
Operating lease, right-of-use assets, net	0.0	0.0
Goodwill and intangible assets, net	0.0	0.0
Investment in consolidated affiliates	(4,437.6)	(4,451.6)
Investment	0.0	0.0
Other non-current assets	0.0	0.0
Total assets	(4,437.6)	(4,451.6)
Current liabilities:
Accounts payable	0.0	0.0
Other current liabilities	0.0	0.0
Total current liabilities	0.0	0.0
Long-term liabilities:
Long-term debt, less current portion	0.0	0.0
Other long-term liabilities	0.0	0.0
Deferred income taxes	0.0	0.0
Total liabilities	0.0	0.0
Interest of non-controlling partner in subsidiary (Note 10)		0.0
Interest of non-controlling partner in subsidiary	0.0
Partners' capital	(4,437.6)	(4,451.6)
Total liabilities and capital	(4,437.6)	(4,451.6)
Parent Company, Crestwood Midstream Partners, LP | Reportable Legal Entities
Current assets:
Cash	0.3	1.8
Accounts receivable	0.0	0.0
Inventory	0.0	0.0
Other	0.0	0.0
Total current assets	0.3	1.8
Property, plant and equipment, net	0.0	0.0
Operating lease, right-of-use assets, net	0.0	0.0
Goodwill and intangible assets, net	0.0	0.0
Investment in consolidated affiliates	4,437.6	4,451.6
Investment	0.0	0.0
Other non-current assets	0.0	0.0
Total assets	4,437.9	4,453.4
Current liabilities:
Accounts payable	0.0	0.0
Other current liabilities	51.5	25.8
Total current liabilities	51.5	25.8
Long-term liabilities:
Long-term debt, less current portion	2,548.9	2,328.3
Other long-term liabilities	0.0	0.0
Deferred income taxes	0.0	0.0
Total liabilities	2,600.4	2,354.1
Interest of non-controlling partner in subsidiary (Note 10)		0.0
Interest of non-controlling partner in subsidiary	0.0
Partners' capital	1,837.5	2,099.3
Total liabilities and capital	4,437.9	4,453.4
Guarantor Subsidiaries | Reportable Legal Entities
Current assets:
Cash	0.0	0.0
Accounts receivable	203.8	229.1
Inventory	100.1	53.7
Other	59.3	54.6
Total current assets	363.2	337.4
Property, plant and equipment, net	2,323.3	2,331.3
Operating lease, right-of-use assets, net	37.0	51.0
Goodwill and intangible assets, net	668.1	650.7
Investment in consolidated affiliates	0.0	0.0
Investment	0.0	0.0
Other non-current assets	2.6	1.9
Total assets	3,394.2	3,372.3
Current liabilities:
Accounts payable	136.2	175.9
Other current liabilities	120.1	123.9
Total current liabilities	256.3	299.8
Long-term liabilities:
Long-term debt, less current portion	0.0	0.0
Other long-term liabilities	159.2	174.8
Deferred income taxes	0.6	0.7
Total liabilities	416.1	475.3
Interest of non-controlling partner in subsidiary (Note 10)		0.0
Interest of non-controlling partner in subsidiary	0.0
Partners' capital	2,978.1	2,897.0
Total liabilities and capital	3,394.2	3,372.3
Non-Guarantor Subsidiaries | Reportable Legal Entities
Current assets:
Cash	13.4	23.6
Accounts receivable	18.3	12.8
Inventory	0.0	0.0
Other	0.2	0.2
Total current assets	31.9	36.6
Property, plant and equipment, net	776.2	736.2
Operating lease, right-of-use assets, net	2.6	2.8
Goodwill and intangible assets, net	280.1	373.4
Investment in consolidated affiliates	0.0	0.0
Investment	953.0	980.4
Other non-current assets	0.5	0.5
Total assets	2,044.3	2,129.9
Current liabilities:
Accounts payable	2.4	10.7
Other current liabilities	22.8	17.6
Total current liabilities	25.2	28.3
Long-term liabilities:
Long-term debt, less current portion	0.0	0.0
Other long-term liabilities	128.0	120.8
Deferred income taxes	0.0	0.0
Total liabilities	153.2	149.1
Interest of non-controlling partner in subsidiary (Note 10)		426.2
Interest of non-controlling partner in subsidiary	431.6
Partners' capital	1,459.5	1,554.6
Total liabilities and capital	2,044.3	2,129.9
Crestwood Midstream Partners LP
Current assets:
Cash	13.7	25.4
Accounts receivable	222.1	241.9
Inventory	100.1	53.7
Other	59.5	54.8
Total current assets	395.4	375.8
Property, plant and equipment, net	3,099.5	3,067.5
Operating lease, right-of-use assets, net	39.6	53.8
Goodwill and intangible assets, net	948.2	1,024.1
Investment in consolidated affiliates	0.0	0.0
Investment	953.0	980.4
Other non-current assets	3.1	2.4
Total assets	5,438.8	5,504.0
Current liabilities:
Accounts payable	138.6	186.6
Other current liabilities	194.4	167.3
Total current liabilities	333.0	353.9
Long-term liabilities:
Long-term debt, less current portion	2,548.9	2,328.3
Other long-term liabilities	287.2	295.6
Deferred income taxes	0.6	0.7
Total liabilities	3,169.7	2,978.5
Interest of non-controlling partner in subsidiary (Note 10)		426.2
Interest of non-controlling partner in subsidiary	431.6
Partners' capital	1,837.5	2,099.3
Total liabilities and capital	$ 5,438.8	$ 5,504.0