Partners' Capital and Distributions (Narrative) (Details) $ / shares in Units, $ in Millions			12 Months Ended
	Jul. 16, 2015 USD ($) shares	Apr. 10, 2015 USD ($) $ / shares shares	Dec. 31, 2014 $ / shares shares	Jun. 30, 2015 $ / shares shares		Mar. 31, 2015 $ / shares	Sep. 30, 2014 $ / shares	Jun. 30, 2014 $ / shares shares	Dec. 31, 2013 shares
Partners Capital And Distributions [Line Items]
Sale of Stock, Price Per Share | $ / shares		$ 44.42
Limited Partners' Capital Accountant, Option To Purchase		600,000
Partners' Capital Account, Public Sale of Units Net of Offering Costs | $		$ 198
Common units, issued		4,600,000	95,029,218	99,629,218
Common units, outstanding			95,029,218	99,629,218				88,691,000	88,691,000
Distribution paid per common unit | $ / shares			$ 0.5800	$ 0.6100	[1]	$ 0.5950	$ 0.5650	$ 0.5500
Class A [Member]
Partners Capital And Distributions [Line Items]
Common units, outstanding				99,589,221
Class B [Member]
Partners Capital And Distributions [Line Items]
Common units, outstanding				39,997
Class Two [Member]
Partners Capital And Distributions [Line Items]
Conversion Feature, Minimum Distribution Coverage Ratio			1.1
Class Three [Member]
Partners Capital And Distributions [Line Items]
Conversion Feature, Minimum Distribution Coverage Ratio			1.1
Class Four [Member]
Partners Capital And Distributions [Line Items]
Conversion Feature, Minimum Distribution Coverage Ratio			1.1
Subsequent Event [Member]
Partners Capital And Distributions [Line Items]
Partners' Capital Account, Public Sale of Units Net of Offering Costs | $	$ 437
Common units, issued	10,350,000

[1] This distribution will be paid to unitholders of record as of July 31, 2015.