Consolidated Balance Sheets (Parenthetical) - $ / shares shares in Millions	Dec. 31, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Preferred stock, shares authorized (in shares)	25.0	25.0
Preferred stock, issued (in shares)	0.0	0.0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	900.0	900.0
Common stock, shares issued (in shares)	395.7	395.7
Treasury stock, shares (in shares)	170.4	155.4