Inventories (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Inventory by Product Type [Abstract]
NGLs		$ 1,120.2		$ 1,120.2		$ 917.4
Petrochemicals and refined products		189.0		189.0		161.5
Crude oil		410.0		410.0		516.3
Natural gas		10.4		10.4		14.6
Total		1,729.6		1,729.6		$ 1,609.8
Summary of cost of sales and lower of cost or net realizable value adjustments [Abstract]
Cost of sales	[1]	6,391.9	$ 4,731.1	13,532.3	$ 10,066.8
Lower of cost or net realizable value adjustments recognized within cost of sales		$ 0.7	$ 2.6	$ 2.6	$ 6.0

[1] Cost of sales is a component of "Operating costs and expenses" as presented on our Unaudited Condensed Statements of Consolidated Operations. Fluctuations in these amounts are primarily due to changes in energy commodity prices and sales volumes associated with our marketing activities.