Stock Based Compensation Plans (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Restricted stock and Restricted stock units outstanding
Granted	$ 18.22	$ 17.01	$ 15.42
Equity Awards [Member]
Restricted stock and Restricted stock units outstanding
Beginning Balance, Shares	0	0	0
Beginning Balance, Weighted Average Exercise Price	$ 0.00	$ 0.00	$ 0.00
Granted	$ 49.56	$ 0.00	$ 0.00
Granted, Shares	331,209	0	0
Vested	$ 49.37	$ 0.00	$ 0.00
Vested, Shares	(88,854)	0	0
Forfeited	$ 49.45	$ 0.00	$ 0.00
Forfeited, Shares	(20,746)	0	0
Ending Balance, Shares	221,609	0	0
Ending Balance, Weighted Average Exercise Price	$ 49.64	$ 0.00	$ 0.00
Liability Awards [Member]
Restricted stock and Restricted stock units outstanding
Beginning Balance, Shares	582,751	627,189	473,547
Beginning Balance, Weighted Average Exercise Price	$ 44.81	$ 45.64	$ 48.50
Granted	$ 51.17	$ 45.83	$ 39.99
Granted, Shares	349,840	413,422	685,578
Vested	$ 45.50	$ 46.90	$ 40.91
Vested, Shares	(416,055)	(439,361)	(521,536)
Forfeited	$ 45.04	$ 46.04	$ 40.83
Forfeited, Shares	(29,292)	(18,499)	(10,400)
Ending Balance, Shares	487,244	582,751	627,189
Ending Balance, Weighted Average Exercise Price	$ 48.76	$ 44.81	$ 45.64