Marketable Securities (Schedule Of Marketable Securities With Gross Unrealized Losses For Which No Other-Than-Temporary Impairment Has Been Incurred) (Details) (Marketable Securities With No OTTI Recognized [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 287.6	$ 92.5
12 Months or More, Fair Value	8.0	7.9
Total, Fair Value	295.6	100.4
Less than 12 Months, Unrealized Loss	(0.4)	(0.1)
12 Months or More, Unrealized Loss	(1.1)	(1.5)
Total, Unrealized Loss	(1.5)	(1.6)
Auction Rate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	0	0
12 Months or More, Fair Value	6.7	6.3
Total, Fair Value	6.7	6.3
Less than 12 Months, Unrealized Loss	0	0
12 Months or More, Unrealized Loss	(1.1)	(1.5)
Total, Unrealized Loss	(1.1)	(1.5)
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	85.7	54.9
12 Months or More, Fair Value	1.2	1.4
Total, Fair Value	86.9	56.3
Less than 12 Months, Unrealized Loss	(0.2)	(0.1)
12 Months or More, Unrealized Loss	0	0
Total, Unrealized Loss	(0.2)	(0.1)
Asset-Backed And Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	43.4	6.7
12 Months or More, Fair Value	0.1	0.2
Total, Fair Value	43.5	6.9
Less than 12 Months, Unrealized Loss	(0.1)	0
12 Months or More, Unrealized Loss	0	0
Total, Unrealized Loss	(0.1)	0
Government And Agency Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	158.5	30.9
12 Months or More, Fair Value	0	0
Total, Fair Value	158.5	30.9
Less than 12 Months, Unrealized Loss	(0.1)	0
12 Months or More, Unrealized Loss	0	0
Total, Unrealized Loss	$ (0.1)	$ 0