Stock-Based Compensation Plans (Details 5) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Summary of stock option activities
Options exercisable	2,348,469	3,593,863
Number of options, Beginning Balance	4,255,985
Options exercised	(1,327,008)
Options forfeited/expired	(18,708)
Number of options, Ending Balance	2,910,269
Weighted Average Exercise Price, Beginning Balance	$ 38.17
Weighted Average Exercise Price of Options exercised	$ 33.11
Weighted Average Exercise Price of forfeited/expired	$ 59.58
Weighted Average Exercise Price, Ending Balance	$ 40.33