Investments (Unrealized Loss Position for Investments) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Current [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 125.7	$ 925.6
Less than 12 Months, Unrealized Losses	(0.4)	(40.4)
12 Months or More, Fair Value	549.7	108.9
12 Months or More, Unrealized Losses	(12.3)	(8.0)
Total, Fair Value	675.4	1,034.5
Total, Unrealized Losses	(12.7)	(48.4)
Current [Member] | Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	45.9	225.3
Less than 12 Months, Unrealized Losses	(0.1)	(7.9)
12 Months or More, Fair Value	151.7	22.5
12 Months or More, Unrealized Losses	(3.6)	(0.8)
Total, Fair Value	197.6	247.8
Total, Unrealized Losses	(3.7)	(8.7)
Current [Member] | U.S. Government and Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value		4.0
Less than 12 Months, Unrealized Losses		0
12 Months or More, Fair Value		0
12 Months or More, Unrealized Losses		0
Total, Fair Value		4.0
Total, Unrealized Losses		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	37.4	453.5
Less than 12 Months, Unrealized Losses	(0.2)	(23.5)
12 Months or More, Fair Value	301.9	79.7
12 Months or More, Unrealized Losses	(6.9)	(6.8)
Total, Fair Value	339.3	533.2
Total, Unrealized Losses	(7.1)	(30.3)
Current [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	42.4	242.8
Less than 12 Months, Unrealized Losses	(0.1)	(9.0)
12 Months or More, Fair Value	96.1	6.7
12 Months or More, Unrealized Losses	(1.8)	(0.4)
Total, Fair Value	138.5	249.5
Total, Unrealized Losses	(1.9)	(9.4)
Noncurrent [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	0	25.4
Less than 12 Months, Unrealized Losses	0	(3.2)
12 Months or More, Fair Value	0.7	34.4
12 Months or More, Unrealized Losses	(0.1)	(4.9)
Total, Fair Value	0.7	59.8
Total, Unrealized Losses	(0.1)	(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	0.7	0.7
12 Months or More, Unrealized Losses	(0.1)	(0.1)
Total, Fair Value	0.7	1.2
Total, Unrealized Losses	(0.1)	(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		7.5
Less than 12 Months, Unrealized Losses		(0.9)
12 Months or More, Fair Value		4.1
12 Months or More, Unrealized Losses		(0.7)
Total, Fair Value		11.6
Total, Unrealized Losses		$ (1.6)