Revenues, Impact of Change in Accounting Policy (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Assets [Abstract]
Accounts receivable - trade, net	$ 3,659.1				$ 4,358.4				$ 3,659.1		$ 4,358.4
Prepaid and other current assets	311.5				312.7				311.5		312.7
Property, plant and equipment, net	38,737.6				35,620.4				38,737.6		35,620.4		$ 33,292.5
Liabilities and Equity
Other current liabilities	404.8				418.6				404.8		418.6
Other long-term liabilities	751.6				578.4				751.6		578.4
Partners' equity	23,853.5				22,547.2				23,853.5		22,547.2
Condensed Consolidated Statement of Operations Information [Abstract]
Revenues	9,182.3	$ 9,585.9	$ 8,467.5	$ 9,298.5	8,426.6	$ 6,886.9	$ 6,607.6	$ 7,320.4	36,534.2	[1]	29,241.5	[2]	23,022.3	[2]
Costs and Expenses [Abstract]
Operating costs and expenses									31,397.3		25,557.5		19,643.5
Operating Activities [Abstract]
Net income	1,305.2	$ 1,334.6	$ 687.2	$ 911.5	$ 797.3	$ 621.3	$ 666.0	$ 771.0	4,238.5		2,855.6		2,553.0
Net effect of changes in operating accounts									16.2		32.2		(180.9)
Investing Activities [Abstract]
Contributions in aid of construction costs									0.0		$ 46.1		$ 41.0
Balances Without Adoption [Member]
Assets [Abstract]
Accounts receivable - trade, net	3,672.4								3,672.4
Prepaid and other current assets	298.2								298.2
Property, plant and equipment, net	38,639.3								38,639.3
Liabilities and Equity
Other current liabilities	404.3								404.3
Other long-term liabilities	664.8								664.8
Partners' equity	23,842.5								23,842.5
Condensed Consolidated Statement of Operations Information [Abstract]
Revenues									35,901.5
Costs and Expenses [Abstract]
Operating costs and expenses									30,775.6
Operating Activities [Abstract]
Net income									4,227.5
Net effect of changes in operating accounts									(71.1)
Investing Activities [Abstract]
Contributions in aid of construction costs									87.3
Impact of Adoption [Member]
Assets [Abstract]
Accounts receivable - trade, net	(13.3)								(13.3)
Prepaid and other current assets	13.3								13.3
Property, plant and equipment, net	98.3								98.3
Liabilities and Equity
Other current liabilities	0.5								0.5
Other long-term liabilities	86.8								86.8
Partners' equity	$ 11.0								11.0
Condensed Consolidated Statement of Operations Information [Abstract]
Revenues									632.7
Costs and Expenses [Abstract]
Operating costs and expenses									621.7
Operating Activities [Abstract]
Net income									11.0
Net effect of changes in operating accounts									87.3
Investing Activities [Abstract]
Contributions in aid of construction costs									(87.3)
Impact of Adoption [Member] | ASC 606 [Member] | Equity NGL Revenue [Member]
Condensed Consolidated Statement of Operations Information [Abstract]
Revenues									621.7
Impact of Adoption [Member] | ASC 606 [Member] | CIAC Revenue [Member]
Condensed Consolidated Statement of Operations Information [Abstract]
Revenues									$ 11.0

[1] Revenues are accounted for under ASC 606 upon implementation at January 1, 2018.

[2] Revenues are accounted for under ASC 605 for historical periods prior to January 1, 2018.