Certain Balance Sheet Information (Accrued Expenses and Other Liabilities) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Accrued Expenses and Other Liabilities [Line Items]
Accrued expenses	$ 51.1	$ 48.3
Accrued property taxes	6.9	8.4
Income tax payable	0.3	0.2
Interest payable	36.7	24.9
Accrued additions to property, plant and equipment	18.1	12.3
Operating leases	14.5	14.7
Finance leases	2.1	2.9
Deferred revenue	10.8	10.3
Total accrued expenses and other liabilities	140.5	122.0
Contract liabilities	183.4	172.2
Operating leases	22.0	28.5
Asset retirement obligations	35.6	34.1
Other long-term liabilities	259.8	253.3
Other
Accrued Expenses and Other Liabilities [Line Items]
Other long-term liabilities	18.8	18.5
Crestwood Midstream Partners LP
Accrued Expenses and Other Liabilities [Line Items]
Accrued expenses	49.9	46.4
Accrued property taxes	6.9	8.4
Income tax payable	0.3	0.2
Interest payable	36.7	24.9
Accrued additions to property, plant and equipment	18.1	12.3
Operating leases	14.5	14.7
Finance leases	2.1	2.9
Deferred revenue	10.8	10.3
Total accrued expenses and other liabilities	139.3	120.1
Contract liabilities	183.4	172.2
Operating leases	22.0	28.5
Asset retirement obligations	35.6	34.1
Other long-term liabilities	256.6	251.8
Crestwood Midstream Partners LP | Other
Accrued Expenses and Other Liabilities [Line Items]
Other long-term liabilities	$ 15.6	$ 17.0