Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Receivables, allowance for doubtful accounts	$ 40	$ 21
Preferred stock,par value	$ 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
Common stock,par value	$ 0.01	$ 0.01
Common stock,shares authorized	250,000,000	250,000,000
Common stock,shares issued	137,081,056	137,028,464
Treasury stock,shares	30,027,146	31,551,170