Supplemental Cash Flow Information (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Decrease (increase) in:
Accounts receivable - trade		$ (1,076.2)	$ (679.0)	$ 1,279.3
Accounts receivable - related parties		(0.7)	0.4	1.3
Inventories		194.6	(871.8)	(72.7)
Prepaid and other current assets		226.0	(49.3)	(59.1)
Other assets		(111.0)	(2.0)	(5.8)
Increase (decrease) in:
Accounts payable - trade		66.6	(21.5)	(52.9)
Accounts payable - related parties		56.0	21.0	(34.8)
Accrued product payables		952.3	1,193.3	(1,342.4)
Accrued interest		17.3	(11.4)	16.5
Other current liabilities		(291.4)	189.9	(67.1)
Other liabilities		(1.3)	49.5	14.4
Net effect of changes in operating accounts		32.2	(180.9)	(323.3)
Cash payments for interest, net of $192.1, $168.2 and $149.1 capitalized in 2017, 2016 and 2015, respectively		912.1	947.9	911.6
Capitalized interest	[1]	192.1	168.2	149.1
Cash payments for federal and state income taxes		20.9	18.7	17.5
Liability for construction in progress expenditures		373.0	124.3	472.8
Sale of Assets:
Proceeds from asset sales		40.1	46.5	1,608.6
Net gains (losses) attributable to asset sales		10.7	2.5	(15.6)
Business Acquisition [Line Items]
Cash paid to acquire business		198.7	1,000.0	1,056.5
Offshore Business [Member]
Sale of Assets:
Proceeds from asset sales		0.0	0.0	1,527.7
Net gains (losses) attributable to asset sales		0.0	0.0	(12.3)
Other Disposal of Assets [Member]
Sale of Assets:
Proceeds from asset sales		40.1	46.5	80.9
Net gains (losses) attributable to asset sales		$ 10.7	2.5	(3.3)
Eagle Ford Midstream Assets [Member]
Business Acquisition [Line Items]
Total consideration for acquisition				2,100.0
Cash paid to acquire business			$ 1,000.0	$ 1,100.0

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