Share-Based Compensation Plans (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2011 M	Dec. 31, 2010	Dec. 31, 2009
Restricted Stock Awards
Share-Based Compensation Plans
Period after which the shares granted will be fully vested (in years)	3 years	3 years	3 years
Unrecognized compensation costs on non-vested awards	$ 3,800,000
Non-Vested Shares
Non-vested shares Outstanding, Beginning of Period	231,900
Shares granted, number	65,390	85,720	62,340
Non-vested shares, Vested	(93,070)
Non-vested shares, Forfeited	(23,270)
Non-vested shares Outstanding, End of Period	180,950	231,900
Aggregate Fair Value
Weighted Average Fair Value, Beginning of Period (in dollars per share)	$ 45.22
Weighted Average Fair Value of shares, Granted (in dollars per share)	$ 51.50	$ 43	$ 33
Weighted Average Fair Value of shares, Vested (in dollars per share)	$ 54.78
Weighted Average Fair Value of shares, Forfeited (in dollars per share)	$ 41.12
Weighted Average Fair Value, End of Period (in dollars per share)	$ 43.10	$ 45.22
Restricted Stock, Aggregate Fair Value
Aggregate Fair Value, Beginning of Period	10,486,005
Aggregate Fair Value of shares, Granted	3,367,478
Aggregate Fair Value of shares, Vested	(5,098,498)	(2,900,000)	(6,000,000)
Aggregate Fair Value of shares, Forfeited	(956,791)
Aggregate Fair Value, End of Period	7,798,194	10,486,005
Non-qualified Stock Options, Aggregate Intrinsic Value
Unrecognized compensation costs on non-vested awards, weighted average period of recognition (in months)	15
Non-Qualified Stock Options
Share-Based Compensation Plans
Unrecognized compensation costs on non-vested awards	2,100,000
Restricted Stock, Weighted Average Remaining Contractual Term (months)
Weighted Average Remaining Contractual Term, End of Period (months/years)	1.5
Assumptions used in the Black-Scholes single option pricing model
Risk-free interest rate (as a percent)	2.02%
Dividend yield (as a percent)	2.19%
Volatility factor (as a percent)	29.00%	28.00%
Expected term (in years)	5	5
Grants in period (in shares)	229,100	409,100
Non-Qualified Stock Options, weighted average grant date fair value (in dollars per share)	$ 10.06	$ 9.31
Non-Qualified Stock Options, total intrinsic value of options exercised	18,300,000	7,500,000	1,600,000
Non-qualified Stock Options, Shares
Non-qualified Stock Options Outstanding, Beginning of Period (in shares)	2,282,276
Non-qualified Stock Options, Granted (in shares)	229,100	409,100
Non-qualified Stock Options, Exercised (in shares)	(561,655)
Non-qualified Stock Options, Forfeited (in shares)	(2,934)
Non-qualified Stock Options Outstanding, End of Period (in shares)	1,946,787	2,282,276
Non-qualified Stock Options Exercisable, End of Period (in shares)	1,710,762
Non-qualified Stock Options, Weighted Average Exercise Price
Weighted Average Exercise Price, Beginning of Period (in dollars per share)	$ 34.31
Weighted Average Exercise Price of shares, Granted (in dollars per share)	$ 44.84
Weighted Average Exercise Price of shares, Exercised (in dollars per share)	$ 17.05
Weighted Average Exercise Price of shares, Forfeited (in dollars per share)	$ 49.17
Weighted Average Exercise Price, End of Period (in dollars per share)	$ 40.51	$ 34.31
Weighted Average Exercise Price of shares, Exercisable (in dollars per share)	$ 40.10
Non-Qualified Stock Options, Weighted Average Remaining Contractual Term
Weighted Average Remaining Contractual Term, End of Period (in years)	5.3
Weighted Average Remaining Contractual Term, Exercisable (in years)	2.9
Non-qualified Stock Options, Aggregate Intrinsic Value
Aggregate Intrinsic Value Outstanding, End of Period	28,154,700
Aggregate Intrinsic Value Exercisable, End of Period	$ 25,445,034
2012 Stock Options
Term of stock options (in years)	5.3
Non-Qualified Stock Options | Minimum
Assumptions used in the Black-Scholes single option pricing model
Risk-free interest rate (as a percent)		1.60%
Dividend yield (as a percent)		2.10%
Non-Qualified Stock Options | Maximum
Assumptions used in the Black-Scholes single option pricing model
Risk-free interest rate (as a percent)		2.50%
Dividend yield (as a percent)		2.34%
2010 Stock Incentive Award program
Share-Based Compensation Plans
Period after which the shares granted will be fully vested (in years)		3 years
Non-Vested Shares
Shares granted, number		155,850
Non-vested shares Outstanding, End of Period	295,635
2012 Value Driver Award Program
Non-Vested Shares
Shares granted, number	265,230
Non-qualified Stock Options, Aggregate Intrinsic Value
Award vested at end of year one, percentage	50.00%
Award vested at end of year two, percentage	50.00%
2012 Value Driver Award Program | Minimum
Non-qualified Stock Options, Aggregate Intrinsic Value
Compensation plan, award as a percentage of target award level	0.00%
2012 Value Driver Award Program | Maximum
Non-qualified Stock Options, Aggregate Intrinsic Value
Compensation plan, award as a percentage of target award level	300.00%
2012 Executive Performance Incentive Plan
Non-Vested Shares
Shares granted, number	377,440
2012 Stock Options
Performance period (in years)	3
2012 Executive Performance Incentive Plan | Minimum
Non-qualified Stock Options, Aggregate Intrinsic Value
Compensation plan, award as a percentage of target award level	0.00%
2012 Executive Performance Incentive Plan | Maximum
Non-qualified Stock Options, Aggregate Intrinsic Value
Compensation plan, award as a percentage of target award level	300.00%
Non-employee Directors' Share-Based Awards
Non-Vested Shares
Shares granted, number	22,140	28,348	23,760
Non-vested shares Outstanding, End of Period	150,423
Aggregate Fair Value
Weighted Average Fair Value of shares, Granted (in dollars per share)	$ 44.84	$ 38.74	$ 41.68
2012 Stock Options
Non-Qualified Stock Options, Weighted Average Remaining Contractual Term
Weighted Average Remaining Contractual Term, End of Period (in years)	10
Non-qualified Stock Options, Aggregate Intrinsic Value
Exercise price of awards (in dollars per share)	$ 54.79
2012 Stock Options
Term of stock options (in years)	10
Exercise price of stock options (in dollars per share)	$ 54.79
Stock options vested at end of year one, percentage	50.00%
Stock options vested at end of year two, percentage	50.00%