Earnings Per Unit (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Numerator:
Net income attributable to limited partners	$ 586.8	$ 471.4	$ 1,804.4	$ 1,325.8
Denominator:
Distribution-bearing common units outstanding (in units)	859.3	821.9	857.9	817.0
Basic earnings per unit:
Net income attributable to limited partners (in dollars per unit)	$ 0.68	$ 0.57	$ 2.10	$ 1.62
Numerator:
Net income attributable to limited partners	$ 586.8	$ 471.4	$ 1,804.4	$ 1,325.8
Denominator:
Distribution-bearing common units outstanding (in units)	859.3	821.9	857.9	817.0
Class B units (in units)	4.5	4.5	4.5	4.5
Designated Units (see Note 10) (in units)	26.1	30.6	26.1	30.6
Incremental option units (in units)	1.5	1.2	1.5	1.2
Total (in units)	891.4	858.2	890.0	853.3
Diluted earnings per unit:
Net income attributable to limited partners (in dollars per unit)	$ 0.66	$ 0.55	$ 2.03	$ 1.55