Certain Balance Sheet Information (Accrued Expenses and Other Liabilities) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Apr. 30, 2019
Accrued Expenses and Other Liabilities [Line Items]
Contract Liabilities (Non-current)	$ 159.6	$ 144.7
Accrued expenses	35.1	61.6
Accrued property taxes	8.2	6.1
Tax payable	0.3	0.3
Interest payable	25.0	25.6
Accrued additions to property, plant and equipment	14.9	38.0
Business Combination, Contingent Consideration, Liability, Current	19.0	0.0
Operating Lease, Liability, Current	17.8	18.1
Capital leases		3.2
Finance Lease, Liability, Current	3.3
Deferred Revenue	10.2	8.8
Total accrued expenses and other liabilities	133.8	161.7
Business Combination, Contingent Consideration, Liability, Noncurrent	38.0	57.0
Long-term operating lease liabilities	32.9	41.5
Asset Retirement Obligations, Noncurrent	34.6	33.3
Other long-term liabilities	285.7	301.6
Crestwood Midstream Partners LP
Accrued Expenses and Other Liabilities [Line Items]
Contract Liabilities (Non-current)	159.6
Accrued expenses	33.7	60.3
Accrued property taxes	8.2	6.1
Tax payable	0.3	0.3
Interest payable	25.0	25.6
Accrued additions to property, plant and equipment	14.9	38.0
Business Combination, Contingent Consideration, Liability, Current	19.0	0.0
Operating Lease, Liability, Current	17.8	18.1
Capital leases		3.2
Finance Lease, Liability, Current	3.3
Deferred Revenue	10.2	8.8
Total accrued expenses and other liabilities	132.4	160.4
Business Combination, Contingent Consideration, Liability, Noncurrent	38.0
Long-term operating lease liabilities	32.9
Asset Retirement Obligations, Noncurrent	34.6
Other long-term liabilities	284.0	295.6
Jackalope Gas Gathering Services, L.L.C.
Accrued Expenses and Other Liabilities [Line Items]
Ownership percentage			50.00%	50.00%
Other Noncurrent Liabilities [Member]
Accrued Expenses and Other Liabilities [Line Items]
Other long-term liabilities	20.6	25.1
Other Noncurrent Liabilities [Member] | Crestwood Midstream Partners LP
Accrued Expenses and Other Liabilities [Line Items]
Other long-term liabilities	$ 18.9	$ 19.1