Earnings Per Unit (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Numerator:
Net income attributable to limited partners	$ 753.5	$ 651.3
Denominator:
Distribution-bearing common units outstanding (in units)	881.6	856.6
Basic earnings per unit:
Net income attributable to limited partners, basic (in dollars per unit)	$ 0.85	$ 0.76
Numerator:
Net income attributable to limited partners	$ 753.5	$ 651.3
Denominator:
Distribution-bearing common units outstanding (in units)	881.6	856.6
Class B units (in units)	4.5	4.5
Designated Units (in units)	23.7	26.1
Incremental option units (in units)	1.2	1.5
Total (in units)	911.0	888.7
Diluted earnings per unit:
Net income attributable to limited partners, diluted (in dollars per unit)	$ 0.83	$ 0.73