Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Current assets
Allowance for doubtful accounts	$ 15.5	$ 5.8
Stockholders' equity
Treasury Stock, shares	11,200,000	14,000,000
Preferred Stock [Member]
Stockholders' equity
Preferred Stock, par value per share	$ 0.01	$ 0.01
Preferred Stock, shares authorized	10,000,000	10,000,000
Preferred Stock, shares issued	0	0
Preferred Stock, shares outstanding	0	0
Perpetual Preferred Stock [Member]
Stockholders' equity
Preferred Stock, shares authorized	800,000	800,000
Preferred Stock, shares issued	0	0
Preferred Stock, shares outstanding	0	0
Series Common Stock [Member]
Stockholders' equity
Common Stock, par value per share	$ 0.01	$ 0.01
Common Stock, shares authorized	40,000,000	40,000,000
Common Stock, shares issued	0	0
Common Stock, shares outstanding	0	0
Common Stock [Member]
Stockholders' equity
Common Stock, par value per share	$ 0.01	$ 0.01
Common Stock, shares authorized	800,000,000	800,000,000
Common Stock, shares issued	289,000,000	285,700,000
Common Stock, shares outstanding	277,800,000	271,400,000