Area dedicated for gas production.

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Capital Commitmentto Acquire Equity Method Investment

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Estimated Cost to Build

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Gas Production Capacity

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Miles of Pipeline

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Percentageof Available Cash Distributed

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Percentage of voting equity interests acquired at the acquisition date in the business combination.

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-Name Accounting Standards Codification
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The amount of the gain (loss) recognized by the parent and included in its attributable portion of net income for the period due to deconsolidation of a subsidiary or derecognition of a group of assets. The gain (loss) recognized and included in the net income attributable to the parent for the period is generally computed as the difference between: (a) the aggregate of: (1) the fair value of any consideration received; (2) the fair value of any retained noncontrolling investment in the former subsidiary at the date the subsidiary was deconsolidated; and (3) the carrying amount of any noncontrolling interest in the former subsidiary (including any accumulated other comprehensive income attributable to the noncontrolling interest) at the date the subsidiary was deconsolidated and (b) the carrying amount of the former subsidiary's assets and liabilities.

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This item represents disclosure of the amount of dividends or other distributions received from unconsolidated subsidiaries, certain corporate joint ventures, and certain noncontrolled corporation; these investments are accounted for under the equity method of accounting. This element excludes distributions that constitute a return of investment, which are classified as investing activities.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

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The cash outflow associated with the purchase of or advances to an equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

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The cash inflow from the sale of property, plant and equipment (capital expenditures), software, and other intangible assets.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Investments in Unconsolidated Affiliates (Detail) $ in Millions	1 Months Ended			3 Months Ended		12 Months Ended
	Feb. 28, 2017 USD ($)	Jan. 31, 2017 USD ($)	Dec. 31, 2014 USD ($)	Mar. 31, 2017 USD ($) a mi MMcf	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($) mi MMcf	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Schedule of Equity Method Investments [Line Items]
Proceeds from sale of assets				$ 0.0	$ 0.8	$ 972.7	$ 2.7	$ 69.1
Investments in unconsolidated affiliates				1,105.3		1,115.4	254.3
Investment in unconsolidated affiliates in period				0.1	5.5	12.4	42.0	108.6
Estimated Cost to Build				180.0		$ 180.0
Proceeds from Equity Method Investment, Dividends or Distributions				$ 18.3	5.7
Stagecoach Gas Services LLC
Schedule of Equity Method Investments [Line Items]
Equity method ownership percentage				50.00%		50.00%
Investments in unconsolidated affiliates				$ 864.9		$ 871.0	0.0
Investment in unconsolidated affiliates in period				0.0	0.0
Percentage of Available Cash Distributed						35.00%
Proceeds from Equity Method Investment, Dividends or Distributions		$ 12.1		$ 12.1	0.0	$ 16.0
Stagecoach Gas Services LLC \| Scenario, Previously Reported
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated affiliates						$ 871.1
Tres Palacios Holdings LLC
Schedule of Equity Method Investments [Line Items]
Equity method ownership percentage				50.01%		50.01%
Investments in unconsolidated affiliates				$ 39.5		$ 39.0	36.8
Deconsolidation, Gain (Loss), Amount			$ 30.6
Investment in unconsolidated affiliates in period			132.8	0.0	5.5
Proceeds from Equity Method Investment, Dividends or Distributions				$ 0.0	0.0	$ 8.5	7.4
Powder River Basin Industrial Complex, LLC
Schedule of Equity Method Investments [Line Items]
Equity method ownership percentage				50.01%		50.01%
Investments in unconsolidated affiliates				$ 8.4		$ 8.7	15.1
Investment in unconsolidated affiliates in period				0.0	0.0		10.7	3.4
Proceeds from Equity Method Investment, Dividends or Distributions		$ 0.4		$ 0.3	0.6	$ 2.0	1.9
Crestwood Permian Basin Holdings [Member]
Schedule of Equity Method Investments [Line Items]
Gas Production Capacity \| MMcf				250		250
Crestwood Permian Basin Holdings [Member] \| Low Pressure Gathering Lines
Schedule of Equity Method Investments [Line Items]
Miles of pipeline \| mi				194		194
Crestwood Permian Basin Holdings [Member] \| High Pressure Trunklines
Schedule of Equity Method Investments [Line Items]
Miles of pipeline \| mi				36		36
Jackalope Gas Gathering Services, LLC
Schedule of Equity Method Investments [Line Items]
Equity method ownership percentage				50.00%		50.00%
Investments in unconsolidated affiliates				$ 193.2		$ 197.2	202.4
Investment in unconsolidated affiliates in period				0.1	0.0
Proceeds from Equity Method Investment, Dividends or Distributions	$ 5.9			5.9	5.1	27.4	12.5
CEGP [Member] \| Stagecoach Gas Services LLC
Schedule of Equity Method Investments [Line Items]
Proceeds from sale of assets						$ 975.0
Percentage of Available Cash Distributed						65.00%
Crestwood Midstream Partners LP
Schedule of Equity Method Investments [Line Items]
Proceeds from sale of assets				0.0	0.8	$ 972.7	2.7	2.7
Investments in unconsolidated affiliates				1,105.3		1,115.4	254.3
Investment in unconsolidated affiliates in period				$ 0.1	$ 5.5	$ 12.4	41.8	144.4
Crestwood Midstream Partners LP \| Stagecoach Gas Services LLC
Schedule of Equity Method Investments [Line Items]
Equity method ownership percentage						50.00%
Deconsolidation, Gain (Loss), Amount						$ 32.4
Crestwood Midstream Partners LP \| Tres Palacios Holdings LLC
Schedule of Equity Method Investments [Line Items]
Equity method ownership percentage						50.01%
Investment in unconsolidated affiliates in period			$ 66.4
Brookfield Infrastructure Group \| Tres Palacios Holdings LLC
Schedule of Equity Method Investments [Line Items]
Equity method ownership percentage						49.99%
Crestwood Equity Partners LP \| Tres Palacios Holdings LLC
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated affiliates							35.8
Crestwood Equity Partners LP \| Crestwood Permian Basin Holdings [Member]
Schedule of Equity Method Investments [Line Items]
Equity method ownership percentage				50.00%		50.00%
Capital Commitment to Acquire Equity Method Investment				$ 37.5		$ 37.5
Twin Eagle Powder River Basin, LLC \| Powder River Basin Industrial Complex, LLC
Schedule of Equity Method Investments [Line Items]
Percentage of voting interests acquired						50.00%
SWEPI LP \| Crestwood Permian Basin Holdings [Member]
Schedule of Equity Method Investments [Line Items]
Equity method ownership percentage				50.00%		50.00%
Area dedicated for gas production \| a				100,000
First Reserve Management, L.P. \| Crestwood Permian Basin Holdings [Member]
Schedule of Equity Method Investments [Line Items]
Capital Commitment to Acquire Equity Method Investment				$ 37.5		$ 37.5
Crestwood Niobrara LLC \| Tres Palacios Holdings LLC
Schedule of Equity Method Investments [Line Items]
Investment in unconsolidated affiliates in period						11.0	5.7
Crestwood Niobrara LLC \| Jackalope Gas Gathering Services, LLC
Schedule of Equity Method Investments [Line Items]
Investment in unconsolidated affiliates in period						$ 1.4	$ 25.4	$ 105.2
Williams Partners LP \| Jackalope Gas Gathering Services, LLC
Schedule of Equity Method Investments [Line Items]
Percentage of voting interests acquired						50.00%