Transactions Affecting Allowance for Doubtful Accounts (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Receivables [Line Items]
Balance, beginning of year	$ 62.6	$ 71.0	$ 70.3
Provisions charged to expense	8.7	18.8	22.8
Write-offs and other	(21.7)	(27.2)	(22.1)
Balance, end of year	$ 49.6	$ 62.6	$ 71.0