Earnings Per Unit (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Numerator:
Net income attributable to limited partners	$ 651.3	$ 420.7
Denominator:
Common units (in units)	852.3	809.9
Time-vested restricted common units (in units)	4.3	4.0
Total (in units)	856.6	813.9
Basic earnings per unit:
Net income attributable to limited partners (in dollars per unit)	$ 0.76	$ 0.52
Numerator:
Net income attributable to limited partners	$ 651.3	$ 420.7
Denominator:
Common units (in units)	852.3	809.9
Time-vested restricted common units (in units)	4.3	4.0
Class B units (in units)	4.5	4.5
Designated Units (in units)	26.1	30.6
Incremental option units (in units)	1.5	1.3
Total (in units)	888.7	850.3
Diluted earnings per unit:
Net income attributable to limited partners (in dollars per unit)	$ 0.73	$ 0.49