Marketable Securities (Schedule Of Available-For-Sale Marketable Securities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 787.4	$ 697.7
Gross Unrealized Gains	2.3	3.6
Gross Unrealized Losses	(1.5)	(1.6)
Estimated Fair Value	788.2	699.7
Auction Rate Securities - Municipal Debt [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3.8	3.8
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(0.4)	(0.5)
Estimated Fair Value	3.4	3.3
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	360.7	301.3
Gross Unrealized Gains	1.6	2.4
Gross Unrealized Losses	(0.2)	(0.1)
Estimated Fair Value	362.1	303.6
Government And Agency Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	358.2	340.2
Gross Unrealized Gains	0.2	0.6
Gross Unrealized Losses	(0.1)	0
Estimated Fair Value	358.3	340.8
Asset-Backed And Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	73.2	55.9
Gross Unrealized Gains	0.5	0.6
Gross Unrealized Losses	(0.1)	0
Estimated Fair Value	73.6	56.5
Total Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	795.9	701.2
Gross Unrealized Gains	2.3	3.6
Gross Unrealized Losses	(0.8)	(0.6)
Estimated Fair Value	797.4	704.2
Auction Rate Securities - Preferred [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4.0	4.0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(0.7)	(1.0)
Estimated Fair Value	3.3	3.0
Total Security Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	799.9	705.2
Gross Unrealized Gains	2.3	3.6
Gross Unrealized Losses	(1.5)	(1.6)
Estimated Fair Value	800.7	707.2
Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	(12.5)	(7.5)
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ (12.5)	$ (7.5)