Investments in Unconsolidated Affiliates (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated affiliates		$ 2,659.4	$ 2,677.3	$ 2,628.5
Equity in income (loss) of unconsolidated affiliates by business segment [Abstract]
Equity in income (loss) of unconsolidated affiliates		426.0	362.0	373.6
Unamortized excess cost amounts by business segment:
Unamortized excess cost amounts		42.9	45.2
Equity method investment amortization of excess cost		2.1	2.1	4.9
Forecasted amortization of excess cost amounts - 2018		2.2
Forecasted amortization of excess cost amounts - 2019		2.2
Forecasted amortization of excess cost amounts - 2020		2.2
Forecasted amortization of excess cost amounts - 2021		2.2
Forecasted amortization of excess cost amounts - 2022		2.2
Balance Sheet Data:
Current assets		288.8	199.5
Property, plant and equipment, net		5,509.7	5,644.4
Other assets		71.2	61.5
Total assets		5,869.7	5,905.4
Current liabilities		233.5	208.5
Other liabilities		84.8	112.3
Combined equity		5,551.4	5,584.6
Total liabilities and combined equity		5,869.7	5,905.4
Income Statement Data:
Revenues		1,509.0	1,342.0	1,426.6
Operating income		925.9	786.7	825.8
Net income		929.5	781.7	814.1
NGL Pipelines & Services [Member]
Equity in income (loss) of unconsolidated affiliates by business segment [Abstract]
Equity in income (loss) of unconsolidated affiliates		73.4	61.4	57.5
Unamortized excess cost amounts by business segment:
Unamortized excess cost amounts		$ 22.9	24.1
NGL Pipelines & Services [Member] | Venice Energy Service Company, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest		13.10%
Investments in unconsolidated affiliates		$ 25.7	24.8
NGL Pipelines & Services [Member] | K/D/S Promix, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest		50.00%
Investments in unconsolidated affiliates		$ 30.9	33.7
NGL Pipelines & Services [Member] | Baton Rouge Fractionators LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest		32.20%
Investments in unconsolidated affiliates		$ 17.0	17.3
NGL Pipelines & Services [Member] | Skelly-Belvieu Pipeline Company, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest		50.00%
Investments in unconsolidated affiliates		$ 37.0	38.9
NGL Pipelines & Services [Member] | Texas Express Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest		35.00%
Investments in unconsolidated affiliates		$ 314.4	331.9
NGL Pipelines & Services [Member] | Texas Express Gathering LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest		45.00%
Investments in unconsolidated affiliates		$ 35.9	35.8
NGL Pipelines & Services [Member] | Front Range Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest		33.30%
Investments in unconsolidated affiliates		$ 165.7	165.4
NGL Pipelines & Services [Member] | Delaware Basin Gas Processing LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest		50.00%
Investments in unconsolidated affiliates		$ 107.3	102.6
Crude Oil Pipelines & Services [Member]
Equity in income (loss) of unconsolidated affiliates by business segment [Abstract]
Equity in income (loss) of unconsolidated affiliates		358.4	311.9	281.4
Unamortized excess cost amounts by business segment:
Unamortized excess cost amounts		$ 18.2	19.0
Crude Oil Pipelines & Services [Member] | Seaway Crude Pipeline Company LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest		50.00%
Investments in unconsolidated affiliates		$ 1,378.9	1,393.8
Crude Oil Pipelines & Services [Member] | Eagle Ford Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest		50.00%
Investments in unconsolidated affiliates		$ 385.2	377.9
Crude Oil Pipelines & Services [Member] | Eagle Ford Terminals Corpus Christi LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest		50.00%
Investments in unconsolidated affiliates		$ 75.1	52.9
Natural Gas Pipelines & Services [Member]
Equity in income (loss) of unconsolidated affiliates by business segment [Abstract]
Equity in income (loss) of unconsolidated affiliates		$ 3.8	3.8	3.8
Natural Gas Pipelines & Services [Member] | White River Hub, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest		50.00%
Investments in unconsolidated affiliates		$ 20.8	21.7
Petrochemical & Refined Products Services [Member]
Equity in income (loss) of unconsolidated affiliates by business segment [Abstract]
Equity in income (loss) of unconsolidated affiliates	[1]	(9.6)	(15.1)	(15.7)
Unamortized excess cost amounts by business segment:
Unamortized excess cost amounts		$ 1.8	2.1
Petrochemical & Refined Products Services [Member] | Centennial Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest		50.00%
Investments in unconsolidated affiliates		$ 60.8	62.3
Petrochemical & Refined Products Services [Member] | Other Unconsolidated Affiliates [Member]
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated affiliates		4.7	18.3
Offshore Pipelines & Services [Member]
Equity in income (loss) of unconsolidated affiliates by business segment [Abstract]
Equity in income (loss) of unconsolidated affiliates		$ 0.0	$ 0.0	$ 46.6	[2]

[1] Losses are primarily attributable to our investment in Centennial. As a result of a trend in declining earnings, we estimated the fair value of this equity-method investment during each of the last three fiscal years. Our estimates, based on a combination of market and income approaches, indicate that the fair value of this investment remains in excess of its carrying value.

[2] Our investments in unconsolidated affiliates classified within the Offshore Pipelines & Services segment were sold in July 2015 (see Note 10).