Initial Public Offering Initial Public Offering (Tables)
 12 Months Ended
Dec. 31, 2015
Initial Public Offering [Abstract]  
Change From Net Income Attributable to the Partnership and Transfers to Noncontrolling Interest
 
Year Ended December 31,
(in millions)
2015
Net income attributable to the Partnership
$
74.0

Decrease in partnership equity for the purchase of an additional 8.4 percent interest in Columbia OpCo
(424.4
)
Change from net income attributable to the Partnership and transfers to noncontrolling interest
$
(350.4
)