Supplementary Balance Sheet Data (Details) (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2010
Supplementary Balance Sheet Data
Accounts receivable - allowance for doubtful accounts	$ 63.7	$ 78.0	$ 74.1
Accounts receivable - allowance for sales returns	233.2	197.3	241.8
Prepublication costs - accumulated amortization	1,038.4	1,089.3	1,057.8
Property and equipment - accumulated depreciation	$ 1,056.8	$ 1,009.2	$ 997.2