Investments (Unrealized Loss Position For Current & Noncurrent Investments) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Current [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 303.0	$ 187.3
Less than 12 Months, Unrealized Losses	(2.7)	(4.3)
12 Months or More, Fair Value	0.3	5.5
12 Months or More, Unrealized Losses	0	(0.2)
Total, Fair Value	303.3	192.8
Total, Unrealized Losses	(2.7)	(4.5)
Current [Member] | Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	54.9	30.5
Less than 12 Months, Unrealized Losses	(0.2)	(0.2)
12 Months or More, Fair Value	0.1	1.1
12 Months or More, Unrealized Losses	0	0
Total, Fair Value	55.0	31.6
Total, Unrealized Losses	(0.2)	(0.2)
Current [Member] | U.S. government and agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	10.1	0
Less than 12 Months, Unrealized Losses	0	0
12 Months or More, Fair Value	0	0
12 Months or More, Unrealized Losses	0	0
Total, Fair Value	10.1	0
Total, Unrealized Losses	0	0
Current [Member] | Obligations of states and other political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	192.1	7.5
Less than 12 Months, Unrealized Losses	(2.0)	0
12 Months or More, Fair Value	0.2	3.0
12 Months or More, Unrealized Losses	0	(0.1)
Total, Fair Value	192.3	10.5
Total, Unrealized Losses	(2.0)	(0.1)
Current [Member] | Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	45.9	149.3
Less than 12 Months, Unrealized Losses	(0.5)	(4.1)
12 Months or More, Fair Value	0	1.4
12 Months or More, Unrealized Losses	0	(0.1)
Total, Fair Value	45.9	150.7
Total, Unrealized Losses	(0.5)	(4.2)
Noncurrent [Member] | Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value		2.1
Less than 12 Months, Unrealized Losses		(0.3)
12 Months or More, Fair Value		0
12 Months or More, Unrealized Losses		0
Total, Fair Value		2.1
Total, Unrealized Losses		$ (0.3)