Summary Of Significant Accounting Policies (Summary Of Nonvested Shares) (Details) (USD $)	1 Months Ended	3 Months Ended
	Jan. 31, 2012	Mar. 31, 2012
Summary Of Significant Accounting Policies [Abstract]
Share Units, Nonvested at January 1, 2012	1,156,831	1,156,831
Share Units, Granted		717,151	[1]
Share Units, Forfeited		(3,897)
Share Units, Vested		(110,729)	[2]
Share Units, Nonvested at March 31, 2012		1,759,356
Weighted-average Fair Value Per Unit, Nonvested at January 1, 2012	$ 31.70	$ 31.70
Weighted-average Fair Value Per Unit, Granted	$ 35.68	$ 35.68	[1]
Weighted-average Fair Value Per Unit, Forfeitures		$ 32.94
Weighted-average Fair Value Per Unit, Vested		$ 35.68	[2]
Weighted-average Fair Value Per Unit, Nonvested at March 31, 2012		$ 33.07

[1] Includes performance share units (share units) granted to certain executive and nonexecutive officers and other eligible employees in January 2012 under the 2006 Plan.

[2] Share units vested due to retirement eligibility by certain employees. Actual shares issued for retirement-eligible employees will vary depending on actual performance over the three-year measurement period.