Supplemental Cash Flow Information (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Decrease (increase) in:
Accounts receivable - trade		$ 730.2	$ (1,076.2)	$ (679.0)
Accounts receivable - related parties		(2.3)	(0.7)	0.4
Inventories		121.4	194.6	(871.8)
Prepaid and other current assets		214.4	226.0	(49.3)
Other assets		(9.7)	(111.0)	(2.0)
Increase (decrease) in:
Accounts payable - trade		18.3	66.6	(21.5)
Accounts payable - related parties		51.4	56.0	21.0
Accrued product payables		(1,132.0)	952.3	1,193.3
Accrued interest		37.6	17.3	(11.4)
Other current liabilities		(70.9)	(291.4)	189.9
Other liabilities		57.8	(1.3)	49.5
Net effect of changes in operating accounts		16.2	32.2	(180.9)
Cash payments for interest, net of $147.9, $192.1 and $168.2 capitalized in 2018, 2017 and 2016, respectively		1,017.9	912.1	947.9
Capitalized interest	[1]	147.9	192.1	168.2
Cash payments for federal and state income taxes		15.5	20.9	18.7
Liability for construction in progress expenditures		567.6	373.0	124.3
Contributions in aid of construction costs		0.0	46.1	41.0
Sale of Assets:
Proceeds from asset sales		161.2	40.1	46.5
Net gains attributable to asset sales		28.7	10.7	2.5
Business Acquisition [Line Items]
Cash paid to acquire business		150.6	198.7	1,000.0
Red River System [Member]
Sale of Assets:
Proceeds from asset sales		134.9	0.0	0.0
Net gains attributable to asset sales		20.6	0.0	0.0
Other Disposal of Assets [Member]
Sale of Assets:
Proceeds from asset sales		26.3	40.1	46.5
Net gains attributable to asset sales		$ 8.1	$ 10.7	2.5
Eagle Ford Midstream Assets [Member]
Business Acquisition [Line Items]
Total consideration for acquisition					$ 2,100.0
Cash paid to acquire business				$ 1,000.0

[1] Capitalized interest is a component of "Interest expense" as presented on our Statements of Consolidated Operations.