Equity (Details) (USD $) In Millions, except Share data, unless otherwise specified			12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Repurchased from employees under stock incentive plan and cancellation of restricted stock	Dec. 31, 2012 Repurchased from employees under stock incentive plan and cancellation of restricted stock	Dec. 31, 2011 Repurchased from employees under stock incentive plan and cancellation of restricted stock	Dec. 31, 2013 Repurchase of common shares on the open market	Dec. 31, 2012 Repurchase of common shares on the open market	Dec. 31, 2011 Repurchase of common shares on the open market	Dec. 31, 2013 New stock repurchase program	Dec. 13, 2013 New stock repurchase program	Dec. 31, 2013 Previous stock repurchase program
Preferred stock:
Authorized shares	25,000,000	25,000,000
Par value per share (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, issued shares	0	0
Preferred stock, outstanding shares	0	0
Treasury stock:
Repurchase of shares			21,629	44,674	73,260	3,385,000	300,000	1,000,000
Average purchase prices of treasury stock (in dollars per share) repurchased from employees under the stock incentive plan and the cancellation of restricted stock			$ 44.55	$ 58.59	$ 47.48
Shares authorized to be repurchased										4,000,000	5,000,000
Cost to repurchase common shares on the open market						$ 227	$ 15	$ 45
Remaining shares available to be repurchased under its program									4,000,000