UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Current assets:
Allowance for doubtful accounts	$ 13.2	$ 13.4
Accumulated amortization	$ 1,022.4	$ 990.4
Common units [Member]
Limited partners:
Capital account, units outstanding (in units)	895,643,795	881,620,418
Class B units [Member]
Limited partners:
Capital account, units outstanding (in units)	4,520,431	4,520,431