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Employee Stock Plans (Tables)
 12 Months Ended
Dec. 31, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block]
The following information relates to the stock option activity for the year ended December 31, 2012:

 
Shares
 
Weighted- Average Exercise Price
 
Weighted- Average Remaining Contractual Life
 
Aggregate Intrinsic Value
Outstanding at December 31, 2011
3,120,266

 
$
30.61

 
 
 
 
 
 
Granted
473,580

 
 
40.10

 
 
 
 
 
 
Exercised
(523,879
)
 
 
25.52

 
 
 
 
 
 
Forfeited
(61,447
)
 
 
33.68

 
 
 
 
 
 
Outstanding at December 31, 2012
3,008,520

 
 
32.93

 
71

months
 
$
16,935

Exercisable at December 31, 2012
1,844,749

 
 
32.16

 
54

months
 
$
11,195


The aggregate intrinsic value in the table above represents the total pre-tax intrinsic value (the difference between the company's closing stock price on the last trading day of 2012 and the exercise price, multiplied by the number of in-the-money options) received by the option holders had all option holders exercised their options on December 31, 2012. This amount changes based on the market value of the company's stock.
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]
The fair value of stock options was estimated using the Black-Scholes valuation model with the following weighted-average assumptions for the years ended December 31:

 
2012
 
2011
 
2010
Volatility (percent) (a)
39

 
37

 
37

Expected term (in years) (b)
5.3

 
5.5

 
5.2

Risk-free interest rate (percent) (c)
1.0

 
2.4

 
2.4


(a)
Volatility is measured using historical daily price changes of the company's common stock over the expected term of the option.
(b)
The expected term represents the weighted-average period the option is expected to be outstanding and is based primarily on the historical exercise behavior of employees.
(c)
The risk-free interest rate is based on the U.S. Treasury zero-coupon yield with a maturity that approximates the expected term of the option.

There is no expected dividend yield.
Schedule of Nonvested Share Activity [Table Text Block]
The following information summarizes the changes in non-vested performance shares, performance units, restricted stock, and restricted stock units for 2012:

 
Shares
 
Weighted- Average Grant Date Fair Value
Non-vested shares at December 31, 2011
2,936,719

 
$
27.76

Granted
865,146

 
 
39.82

Vested
(867,228
)
 
 
23.78

Forfeited
(149,984
)
 
 
31.26

Non-vested shares at December 31, 2012
2,784,653

 
 
32.56