Fair Value Measurements (Schedule of Carrying Values and Estimated Fair Values of Senior Notes) (Details) - Crestwood Midstream Partners LP - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
2023 Senior Notes
Debt Instrument [Line Items]
Carrying Amount	$ 0.0	$ 683.8
Fair Value	0.0	691.5
2025 Senior Notes
Debt Instrument [Line Items]
Carrying Amount	496.3	495.5
Fair Value	511.9	509.9
2027 Senior Notes
Debt Instrument [Line Items]
Carrying Amount	594.0	593.2
Fair Value	618.4	594.1
Senior Notes, 2029
Debt Instrument [Line Items]
Carrying Amount	690.5	0.0
Fair Value	$ 734.0	$ 0.0