UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Current assets:
Accounts receivable, allowance for doubtful accounts	$ 14.0	$ 12.1
Intangible assets, accumulated amortization	$ 1,365.9	$ 1,235.8
Limited partners:
Common units outstanding (in units)	2,102,796,228	2,012,553,024