UNAUDITED CONDENSED STATEMENTS OF CONSOLIDATED EQUITY (USD $) In Millions, unless otherwise specified	Limited Partners [Member]	Accumulated Other Comprehensive Income Loss [Member]	Noncontrolling Interests [Member]	Total
Balance at Dec. 31, 2010	$ 11,406.7	$ (32.5)	$ 526.6	$ 11,900.8
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income	1,325.8	0	36.7	1,362.5
Cash distributions paid to limited partners	(1,459.7)	0	0	(1,459.7)
Cash distributions paid to noncontrolling interests	0	0	(52.0)	(52.0)
Cash contributions from noncontrolling interests	0	0	4.7	4.7
Net cash proceeds from issuance of common units	67.1	0	0	67.1
Amortization of fair value of equity-based awards	37.9	0	0.1	38.0
Issuance of common units pursuant to Duncan Merger (see Note 1)	402.8	(1.1)	(401.7)	0
Cash flow hedges	0	(301.9)	0	(301.9)
Other	(5.1)	(1.3)	(1.6)	(8.0)
Balance at Sep. 30, 2011	11,775.5	(336.8)	112.8	11,551.5
Balance at Dec. 31, 2011	12,464.8	(351.4)	105.9	12,219.3
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income	1,804.4	0	6.2	1,810.6
Cash distributions paid to limited partners	(1,613.4)	0	0	(1,613.4)
Cash distributions paid to noncontrolling interests	0	0	(11.3)	(11.3)
Cash contributions from noncontrolling interests	0	0	6.5	6.5
Net cash proceeds from issuance of common units	654.8	0	0	654.8
Amortization of fair value of equity-based awards	45.9	0	0	45.9
Cash flow hedges	0	(40.4)	0	(40.4)
Other	(18.6)	3.5	1.0	(14.1)
Balance at Sep. 30, 2012	$ 13,337.9	$ (388.3)	$ 108.3	$ 13,057.9