Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Allowance for doubtful accounts	$ 121.5	$ 121.4
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	2,000.0	2,000.0
Common stock, shares issued	785.7	774.6
Common stock, shares outstanding	698.1	687.5