UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Current assets:
Accounts receivable, allowance for doubtful accounts	$ 12.1	$ 11.3
Intangible assets, accumulated amortization	$ 1,483.9	$ 1,403.1
Limited partners:
Common units outstanding (in units)	2,148,035,389	2,117,588,414