Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Millions, $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Allowance for doubtful accounts	$ 22.5	$ 24.9
Accumulated depreciation	1,206.6	1,221.2
Intangible assets, accumulated amortization	$ 680.7	$ 611.4
Preferred stock, par value	$ 1.00	$ 1.00
Preferred stock, shares authorized	7.5	7.5
Preferred stock, shares issued	0.0	0.0
Common stock, par value	$ 0.15	$ 0.15
Common stock, shares authorized	1,000.0	1,000.0
Common stock, shares issued	397.2	397.2
Common stock, shares outstanding	239.7	246.7
Treasury stock, shares	157.5	150.5