Initial Public Offering (Schedule of Change From Net Income Attributable to the Partnership and Transfers to Noncontrolling Interest) (Details) (USD $)
In Millions, unless otherwise specified
 2 Months Ended
Mar. 31, 2015
Initial Public Offering [Line Items]  
Net Income (Loss) Allocated to Limited Partners $ 13.3
Noncontrolling Interest, Increase from Subsidiary Equity Issuance 0 [1]
Change from net income attributable to the Partnership and transfers to noncontrolling interest (411.1)
Noncontrolling Interest [Member]  
Initial Public Offering [Line Items]  
Noncontrolling Interest, Increase from Subsidiary Equity Issuance $ 424.4 [1]
[1] Represents the purchase of an additional 8.4% limited partner interest in Columbia OpCo, recorded at the historical carrying value of Columbia OpCo’s net assets after giving effect to the $1,168.4 million equity contribution.