UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Current assets:
Allowance for doubtful accounts	$ 13.0	$ 13.4
Accumulated amortization	$ 987.9	$ 990.4
Common units [Member]
Limited partners:
Capital account, units outstanding (in units)	883,831,574	881,620,418
Class B units [Member]
Limited partners:
Capital account, units outstanding (in units)	4,520,431	4,520,431