Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) (USD $) In Millions, except Per Share data	Jun. 30, 2011	Dec. 31, 2010
Assets
Accumulated depreciation	$ 412.7	$ 383.6
Accumulated amortization	$ 472.0	$ 441.2
Stockholders' equity:
Preferred stock, par value	$ 1.00	$ 1.00
Preferred stock, shares authorized	10.0	10.0
Preferred stock, shares issued	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	2,000	2,000
Common stock, shares issued	627.5	654.0
Common stock, shares outstanding	627.5	654.0