Condensed Consolidating Financial Information (Statements Of Cash Flows) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities	$ 183.4	$ 193.9
Cash flows from investing activities:
Acquisition, net of cash acquired	162.3	462.1
Purchases of property, plant and equipment	(143.2)	(204.7)
Investments in unconsolidated affiliates	(6.0)	(40.9)
Capital distributions from unconsolidated affiliates	18.9	24.2
Other	(0.3)	(0.5)
Net cash used in investing activities	(292.9)	(684.0)
Cash flows from financing activities:
Proceeds from the issuance of long-term debt	742.5	1,544.0
Payments on long-term debt	(498.2)	(1,159.5)
Payments on finance leases	(1.6)	(1.9)
Payments for debt-related deferred costs	0.0	(9.0)
Net proceeds from issuance of non-controlling interest	2.8	235.0
Distributions to partners	(91.0)	(86.2)
Taxes paid for unit-based compensation vesting	(15.5)	(10.6)
Net cash provided by financing activities	90.5	475.0
Net change in cash	(19.0)	(15.1)
Cash at beginning of period	25.7	17.2
Cash at end of period	6.7	2.1
Eliminations
Cash flows from operating activities	0.0	0.0
Cash flows from investing activities:
Acquisition, net of cash acquired	0.0	0.0
Purchases of property, plant and equipment	0.0	0.0
Investments in unconsolidated affiliates	0.0	0.0
Capital distributions from unconsolidated affiliates	0.0	0.0
Capital distributions from consolidated affiliates	(8.2)	217.1
Other	0.0	0.0
Net cash used in investing activities	(8.2)	217.1
Cash flows from financing activities:
Proceeds from the issuance of long-term debt	0.0	0.0
Payments on long-term debt	0.0	0.0
Payments on finance leases	0.0	0.0
Payments for debt-related deferred costs		0.0
Net proceeds from issuance of non-controlling interest	0.0	0.0
Distributions to partners	0.0	0.0
Contributions from (distributions to) parent	8.2	(217.1)
Taxes paid for unit-based compensation vesting	0.0	0.0
Change in intercompany balances	0.0	0.0
Net cash provided by financing activities	8.2	(217.1)
Net change in cash	0.0	0.0
Cash at beginning of period	0.0	0.0
Cash at end of period	0.0	0.0
Non-Guarantor Subsidiaries | Reportable Legal Entities
Cash flows from operating activities	80.1	(27.3)
Cash flows from investing activities:
Acquisition, net of cash acquired	0.0	462.1
Purchases of property, plant and equipment	(87.0)	(77.0)
Investments in unconsolidated affiliates	(6.0)	(40.9)
Capital distributions from unconsolidated affiliates	18.9	24.2
Capital distributions from consolidated affiliates	0.0	0.0
Other	0.0	0.0
Net cash used in investing activities	(74.1)	(555.8)
Cash flows from financing activities:
Proceeds from the issuance of long-term debt	0.0	0.0
Payments on long-term debt	0.0	0.0
Payments on finance leases	0.0	0.0
Payments for debt-related deferred costs		0.0
Net proceeds from issuance of non-controlling interest	2.8	235.0
Distributions to partners	(18.5)	(6.6)
Contributions from (distributions to) parent	(8.2)	217.1
Taxes paid for unit-based compensation vesting	0.0	0.0
Change in intercompany balances	0.0	137.7
Net cash provided by financing activities	(23.9)	583.2
Net change in cash	(17.9)	0.1
Cash at beginning of period	23.6	0.0
Cash at end of period	5.7	0.1
Parent Company, Crestwood Midstream Partners, LP | Reportable Legal Entities
Cash flows from operating activities	(96.4)	(87.1)
Cash flows from investing activities:
Acquisition, net of cash acquired	0.0	0.0
Purchases of property, plant and equipment	0.0	0.0
Investments in unconsolidated affiliates	0.0	0.0
Capital distributions from unconsolidated affiliates	0.0	0.0
Capital distributions from consolidated affiliates	8.2	(217.1)
Other	0.0	0.0
Net cash used in investing activities	8.2	(217.1)
Cash flows from financing activities:
Proceeds from the issuance of long-term debt	742.5	1,544.0
Payments on long-term debt	(498.2)	(1,159.1)
Payments on finance leases	0.0	0.0
Payments for debt-related deferred costs		(9.0)
Net proceeds from issuance of non-controlling interest	0.0	0.0
Distributions to partners	(119.0)	(117.5)
Contributions from (distributions to) parent	0.0	0.0
Taxes paid for unit-based compensation vesting	0.0	0.0
Change in intercompany balances	(38.5)	30.7
Net cash provided by financing activities	86.8	289.1
Net change in cash	(1.4)	(15.1)
Cash at beginning of period	1.8	16.5
Cash at end of period	0.4	1.4
Crestwood Midstream Partners LP
Cash flows from operating activities	181.1	195.1
Cash flows from investing activities:
Acquisition, net of cash acquired	162.3	462.1
Purchases of property, plant and equipment	(143.2)	(204.7)
Investments in unconsolidated affiliates	(6.0)	(40.9)
Capital distributions from unconsolidated affiliates	18.9	24.2
Capital distributions from consolidated affiliates	0.0	0.0
Other	(0.3)	(0.5)
Net cash used in investing activities	(292.9)	(684.0)
Cash flows from financing activities:
Proceeds from the issuance of long-term debt	742.5	1,544.0
Payments on long-term debt	(498.2)	(1,159.5)
Payments on finance leases	(1.6)	(1.9)
Payments for debt-related deferred costs		(9.0)
Net proceeds from issuance of non-controlling interest	2.8	235.0
Distributions to partners	(137.5)	(124.1)
Contributions from (distributions to) parent	0.0	0.0
Taxes paid for unit-based compensation vesting	(15.5)	(10.6)
Change in intercompany balances	0.0	0.0
Net cash provided by financing activities	92.5	473.9
Net change in cash	(19.3)	(15.0)
Cash at beginning of period	25.4	16.5
Cash at end of period	6.1	1.5
Guarantor Subsidiaries | Reportable Legal Entities
Cash flows from operating activities	197.4	309.5
Cash flows from investing activities:
Acquisition, net of cash acquired	162.3	0.0
Purchases of property, plant and equipment	(56.2)	(127.7)
Investments in unconsolidated affiliates	0.0	0.0
Capital distributions from unconsolidated affiliates	0.0	0.0
Capital distributions from consolidated affiliates	0.0	0.0
Other	(0.3)	(0.5)
Net cash used in investing activities	(218.8)	(128.2)
Cash flows from financing activities:
Proceeds from the issuance of long-term debt	0.0	0.0
Payments on long-term debt	0.0	(0.4)
Payments on finance leases	(1.6)	(1.9)
Payments for debt-related deferred costs		0.0
Net proceeds from issuance of non-controlling interest	0.0	0.0
Distributions to partners	0.0	0.0
Contributions from (distributions to) parent	0.0	0.0
Taxes paid for unit-based compensation vesting	(15.5)	(10.6)
Change in intercompany balances	38.5	(168.4)
Net cash provided by financing activities	21.4	(181.3)
Net change in cash	0.0	0.0
Cash at beginning of period	0.0	0.0
Cash at end of period	$ 0.0	$ 0.0