UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Current assets:
Accounts receivable, allowance for doubtful accounts	$ 14.3	$ 13.9
Intangible assets, accumulated amortization	$ 1,285.1	$ 1,246.3
Limited partners:
Capital account, units outstanding (in units)	1,988,553,334	1,937,324,817