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Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - shares
shares in Millions
Mar. 31, 2018
Dec. 31, 2017
Statement of Financial Position [Abstract]    
Common units issued 54.3 54.2
Common units outstanding 54.3 54.2
Preferred units issued 14.0 14.0
Preferred units outstanding 14.0 14.0