UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Current assets:
Accounts receivable, allowance for doubtful accounts	$ 11.9	$ 12.1
Intangible assets, accumulated amortization	$ 1,282.1	$ 1,235.8
Limited partners:
Capital account, units outstanding (in units)	2,055,907,178	2,012,553,024