CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
ASSETS
Accounts receivable, allowance for doubtful accounts	$ 11.5	$ 12.1
Intangible assets, accumulated amortization	$ 1,735.1	$ 1,564.8
Limited partners:
Common units outstanding (in units)	2,184,869,029	2,161,089,479