Agreement of Limited Partnership (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	0 Months Ended	6 Months Ended		3 Months Ended						6 Months Ended	3 Months Ended										6 Months Ended			3 Months Ended
	Aug. 06, 2014	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Minimum Quarterly Distributions	Jun. 30, 2014 First Target	Jun. 30, 2014 Second Target	Jun. 30, 2014 Third Target	Jun. 30, 2014 Final Target and Beyond	Jun. 30, 2014 Final Target and Beyond Minimum	Jun. 30, 2014 Common and Class B Common Units	Jun. 30, 2014 Common Units Minimum Quarterly Distributions	Jun. 30, 2014 Common Units First Target	Jun. 30, 2014 Common Units Second Target	Jun. 30, 2014 Common Units Third Target	Jun. 30, 2014 Common Units Final Target and Beyond	Jun. 30, 2014 Class B Common Units Minimum Quarterly Distributions	Jun. 30, 2014 Class B Common Units First Target	Jun. 30, 2014 Class B Common Units Second Target	Jun. 30, 2014 Class B Common Units Third Target	Jun. 30, 2014 Class B Common Units Final Target and Beyond	Jun. 30, 2014 General Partner	Jun. 30, 2014 General Partner Minimum	Jun. 30, 2014 General Partner Maximum	Jun. 30, 2014 General Partner Minimum Quarterly Distributions	Jun. 30, 2014 General Partner First Target	Jun. 30, 2014 General Partner Second Target	Jun. 30, 2014 General Partner Third Target	Jun. 30, 2014 General Partner Final Target and Beyond
Agreement of limited partnership
Partnership distributions paid		$ 156.1	$ 274.6
Available cash received from operating partnership (as a percent)		99.00%
Available cash distributed from operating partnership to General Partner (as a percent)																					1.00%
Cash distribution made, excluding when cumulative distribution is specified, (as a percent)										99.975%											0.025%
Cash distribution declared per common limited partnership unit (in dollars per unit)	$ 3.11
Target Limit				0.605	0.715	0.825	1.045		1.045
Target Increment				0.605	0.110	0.110	0.220
Income and distribution allocation (as a percent)				100.00%	100.00%	100.00%	100.00%	100.00%			98.99%	98.99%	85.859%	75.758%	50.505%	0.985%	0.985%	0.985%	0.985%	0.985%				0.025%	0.025%	13.156%	23.257%	48.51%
Partnership equity interest (as a percent)																					1.00%
Percentage of outstanding units owned by the General Partner and its affiliates																					75.30%
Percentage of ownership of non-affiliates of the General Partner allowing majority owner to acquire outstanding units held by non-affiliated persons																							25.00%
Notice period for making decision to purchase the outstanding units																						30 days	60 days
Number of average trading days' closing prices used to determine the purchase price of outstanding units of non-affiliates		20 days
Number of days before the purchase announcement is made, as a basis for determining the purchase price of outstanding units of non-affiliates		5 days
Period within which highest price is paid for any unit preceding the date the purchase is announced used to determine the purchase price of outstanding units of non-affiliates																					90 days