Earnings Per Unit (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
BASIC EARNINGS PER UNIT
Net income attributable to limited partners	$ 636.1		$ 798.8
Undistributed earnings allocated and cash payments on phantom unit awards	(2.2)	[1]	(1.5)	[1]
Net income available to common unitholders	633.9		797.3
Basic weighted-average number of common units outstanding (in units)	1,926.4		1,828.0
Basic earnings per unit (in dollars per unit)	$ 0.33		$ 0.44
DILUTED EARNINGS PER UNIT
Net income attributable to limited partners	$ 636.1		$ 798.8
Diluted weighted-average number of units outstanding:
Distribution-bearing common units (in units)	1,926.4		1,828.0
Designated Units (in units)	35.4		45.1
Phantom units (in units)	4.5	[1]	1.6	[1]
Incremental option units (in units)	0.4		1.2
Total (in units)	1,966.7		1,875.9
Diluted earnings per unit (in dollars per unit)	$ 0.32		$ 0.43

[1] Each phantom unit award includes a DER, which entitles the recipient to receive cash payments equal to the product of the number of phantom unit awards and the cash distribution per unit paid to our common unitholders. Cash payments made in connection with DERs are nonforfeitable. As a result, the phantom units are considered participating securities for purposes of computing basic earnings per unit. Phantom unit awards were first issued in February 2014.