Share-based Compensation (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Restricted Stock Awards
Options Outstanding
Weighted average fair value of options granted during the year	$ 17,386,949	$ 7,023,942	$ 21,768,084
Summary of restricted stock
Balance at beginning of year (in shares)	2,804,901	2,912,456	2,728,290
Granted (in shares)	192,563	92,729	185,333
Cancelled (in shares)	(3,267)	(200,284)	(1,167)
Balance at end of period (in shares)	2,994,197	2,804,901	2,912,456
Vested during the period (in shares)	21,074	408,800	66,299
Compensation expense recorded	6,713,155	6,930,381	17,365,401
Weighted average fair value of restricted stock granted during the year	17,386,949	7,023,942	21,768,084
Stock options
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Dividend yield (as a percent)	1.92%	2.00%	2.00%
Expected life of option	4 years 1 month 6 days	3 years 8 months 12 days	4 years 2 months 12 days
Risk-free interest rate (as a percent)	0.96%	0.46%	1.00%
Expected stock price volatility (as a percent)	36.12%	37.40%	47.98%
Options Outstanding
Balance at beginning of year (in shares)	1,201,000	1,277,200	1,353,002
Granted (in shares)	828,100	361,331	212,400
Exercised (in shares)	(223,531)	(382,612)	(243,901)
Lapsed or cancelled (in shares)	(40,535)	(54,919)	(44,301)
Balance at end of period (in shares)	1,765,034	1,201,000	1,277,200
Options exercisable at end of period (in shares)	461,458	479,913	644,429
Weighted average fair value of options granted during the year	18,041,576	6,602,967	4,647,554
Weighted Average Exercise Price
Balance at beginning of year (in dollars per share)	$ 75.05	$ 63.37	$ 58.85
Granted (in dollars per share)	$ 87.23	$ 75.36	$ 66.42
Exercised (in dollars per share)	$ 53.93	$ 36.65	$ 40.48
Lapsed or cancelled (in dollars per share)	$ 83.94	$ 72.99	$ 65.89
Balance at end of period (in dollars per share)	$ 83.24	$ 75.05	$ 63.37
Options exercisable at end of period (in dollars per share)	$ 89.38	$ 86.85	$ 72.31
Summary of restricted stock
Compensation expense recorded	6,500,000	5,100,000	4,700,000
Weighted average fair value of restricted stock granted during the year	$ 18,041,576	$ 6,602,967	$ 4,647,554