Stock-Based Compensation (Summary Of Activity In Corporation's Active Stock Plans) (Detail) (USD $)	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012 Stock Options Outstanding [Member]	Sep. 30, 2012 Non-Vested Stock Awards/Stock Units Outstanding [Member]	Dec. 31, 2011 Non-Vested Stock Awards/Stock Units Outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Shares Available for Grant	1,963,455
Granted, Shares Available for Grant	(5,632)
Forfeited, Shares Available for Grant	19,000
Cancelled/expired, Shares Available for Grant	(250)
Ending Balance, Shares Available for Grant	1,976,573
Beginning Balance, Director Deferred Stock Units Outstanding	22,092
Granted, Director Deferred Stock Units Outstanding	5,632
Ending Balance, Director Deferred Stock Units Outstanding	27,724
Beginning Balance, Number of Shares		4,968,822	169,530	169,530
Stock options exercised, Number of Shares		(197,961)
Forfeited, Number of Shares		(19,000)
Ending Balance, Number of Shares		4,751,861	169,530	169,530
Balance, January 1, 2012		$ 51.49	$ 50.33	$ 50.33
Stock options exercised		$ 50.98
Forfeited		$ 50.51
Balance, September 30, 2012		$ 51.51	$ 50.33	$ 50.33