Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Millions, $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 134.2	$ 120.3
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	801.6	792.5
Common stock, shares outstanding	686.8	704.3