Earnings Per Common Share (Summary Of Calculation Of Basic And Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Common Share [Abstract]
Net income used for basic and diluted calculation	$ 578.1	$ 467.6	$ 67.6	$ 1,515.3
Shares used in computing earnings per common share—basic (in shares)	219.1	223.3	220.4	223.8
Stock awards (in shares)	1.5	1.2	1.5	1.6
Shares used in computing earnings per common share-diluted (in shares)	220.6	224.5	221.9	225.4
Earnings per common share
Basic (in dollars per share)	$ 2.64	$ 2.09	$ 0.31	$ 6.77
Diluted (in dollars per share)	$ 2.62	$ 2.08	$ 0.30	$ 6.72