CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
ASSETS
Accounts receivable, allowance for doubtful accounts	$ 12.1	$ 11.3
Intangible assets, accumulated amortization	$ 1,564.8	$ 1,403.1
Limited partners:
Common units outstanding (in units)	2,161,089,479	2,117,588,414