Investments (Unrealized Loss Position For Current & Noncurrent Investments) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Current [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 506.4	$ 925.6
Less than 12 Months, Unrealized Losses	(4.5)	(40.4)
12 Months or More, Fair Value	273.3	108.9
12 Months or More, Unrealized Losses	(4.4)	(8.0)
Total, Fair Value	779.7	1,034.5
Total, Unrealized Losses	(8.9)	(48.4)
Current [Member] | Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	149.3	225.3
Less than 12 Months, Unrealized Losses	(0.5)	(7.9)
12 Months or More, Fair Value	112.5	22.5
12 Months or More, Unrealized Losses	(1.4)	(0.8)
Total, Fair Value	261.8	247.8
Total, Unrealized Losses	(1.9)	(8.7)
Current [Member] | U.S. government and agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	20.7	4.0
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	20.7	4.0
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	37.3	453.5
Less than 12 Months, Unrealized Losses	(0.1)	(23.5)
12 Months or More, Fair Value	104.8	79.7
12 Months or More, Unrealized Losses	(1.6)	(6.8)
Total, Fair Value	142.1	533.2
Total, Unrealized Losses	(1.7)	(30.3)
Current [Member] | Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	299.1	242.8
Less than 12 Months, Unrealized Losses	(3.9)	(9.0)
12 Months or More, Fair Value	56.0	6.7
12 Months or More, Unrealized Losses	(1.4)	(0.4)
Total, Fair Value	355.1	249.5
Total, Unrealized Losses	(5.3)	(9.4)
Noncurrent [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	4.0	25.4
Less than 12 Months, Unrealized Losses	(0.7)	(3.2)
12 Months or More, Fair Value	0.6	34.4
12 Months or More, Unrealized Losses	(0.2)	(4.9)
Total, Fair Value	4.6	59.8
Total, Unrealized Losses	(0.9)	(8.1)
Noncurrent [Member] | Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	0	0.5
Less than 12 Months, Unrealized Losses	0	(0.1)
12 Months or More, Fair Value	0.6	0.7
12 Months or More, Unrealized Losses	(0.2)	(0.1)
Total, Fair Value	0.6	1.2
Total, Unrealized Losses	(0.2)	(0.2)
Noncurrent [Member] | Obligations of states and other political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value		17.4
Less than 12 Months, Unrealized Losses		(2.2)
12 Months or More, Fair Value		29.6
12 Months or More, Unrealized Losses		(4.1)
Total, Fair Value		47.0
Total, Unrealized Losses		(6.3)
Noncurrent [Member] | Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	4.0	7.5
Less than 12 Months, Unrealized Losses	(0.7)	(0.9)
12 Months or More, Fair Value	0	4.1
12 Months or More, Unrealized Losses	0	(0.7)
Total, Fair Value	4.0	11.6
Total, Unrealized Losses	$ (0.7)	$ (1.6)