Stock-Based Compensation (Schedule of Other Stock-Based Awards Activity) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011
Time-Vested Restricted Share Units [Member]
Nonvested at January 1, 2011, Shares	627
Granted, Shares	130
Vested, Shares	(460)
Forfeited, Shares	(21)
Nonvested at December 31, 2011, Shares	276
Nonvested at January 1, 2011, Weighted-Average Grant-Date Fair Value	$ 61.35
Granted, Weighted-Average Grant-Date Fair Value	$ 65.60
Vested, Weighted-Average Grant-Date Fair Value	$ 62.75
Forfeited, Weighted-Average Grant-Date Fair Value	$ 60.56
Nonvested at December 31, 2011, Weighted-Average Grant-Date Fair Value	$ 61.07
Performance-Based Restricted Share Units [Member]
Nonvested at January 1, 2011, Shares	2,170
Granted, Shares	1,040
Vested, Shares	(108)
Forfeited, Shares	(704)
Nonvested at December 31, 2011, Shares	2,398
Nonvested at January 1, 2011, Weighted-Average Grant-Date Fair Value	$ 57.71
Granted, Weighted-Average Grant-Date Fair Value	$ 64.93
Vested, Weighted-Average Grant-Date Fair Value	$ 62.68
Forfeited, Weighted-Average Grant-Date Fair Value	$ 62.98
Nonvested at December 31, 2011, Weighted-Average Grant-Date Fair Value	$ 59.08