Earnings Per Share (Excluded from Diluted Earnings Per Share Calculation) (Details) - $ / shares shares in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted-average number of shares	0.2	0.2
Price range per share (in dollars per share)	$ 205.53	$ 156.94
Minimum [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Price range per share (in dollars per share)		156.94
Maximum [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Price range per share (in dollars per share)		$ 156.94

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic net Income or Loss per outstanding limited partnership unit in the future and that were not included in the computation of diluted net income per limited partnership unit, because to do so would increase net income per unit amounts or decrease loss per unit amounts for the period presented.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=96947427&loc=d3e1533-109256

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=96947427&loc=d3e1536-109256

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Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration