Investments (Unrealized Loss Position For Current & Noncurrent Investments) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Current [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 1,083.3	$ 506.4
Less than 12 Months, Unrealized Losses	(15.4)	(4.5)
12 Months or More, Fair Value	81.0	273.3
12 Months or More, Unrealized Losses	(2.2)	(4.4)
Total, Fair Value	1,164.3	779.7
Total, Unrealized Losses	(17.6)	(8.9)
Current [Member] | Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	437.6	149.3
Less than 12 Months, Unrealized Losses	(5.2)	(0.5)
12 Months or More, Fair Value	34.0	112.5
12 Months or More, Unrealized Losses	(0.6)	(1.4)
Total, Fair Value	471.6	261.8
Total, Unrealized Losses	(5.8)	(1.9)
Current [Member] | U.S. government and agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	28.2	20.7
Less than 12 Months, Unrealized Losses	(0.1)	0.0
12 Months or More, Fair Value	0.0	0.0
12 Months or More, Unrealized Losses	0.0	0.0
Total, Fair Value	28.2	20.7
Total, Unrealized Losses	(0.1)	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	88.5	37.3
Less than 12 Months, Unrealized Losses	(0.7)	(0.1)
12 Months or More, Fair Value	19.7	104.8
12 Months or More, Unrealized Losses	(0.7)	(1.6)
Total, Fair Value	108.2	142.1
Total, Unrealized Losses	(1.4)	(1.7)
Current [Member] | Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	529.0	299.1
Less than 12 Months, Unrealized Losses	(9.4)	(3.9)
12 Months or More, Fair Value	27.3	56.0
12 Months or More, Unrealized Losses	(0.9)	(1.4)
Total, Fair Value	556.3	355.1
Total, Unrealized Losses	(10.3)	(5.3)
Noncurrent [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	18.0	4.0
Less than 12 Months, Unrealized Losses	(4.3)	(0.7)
12 Months or More, Fair Value	9.6	0.6
12 Months or More, Unrealized Losses	(2.3)	(0.2)
Total, Fair Value	27.6	4.6
Total, Unrealized Losses	(6.6)	(0.9)
Noncurrent [Member] | Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value		0.0
Less than 12 Months, Unrealized Losses		0.0
12 Months or More, Fair Value		0.6
12 Months or More, Unrealized Losses		(0.2)
Total, Fair Value		0.6
Total, Unrealized Losses		(0.2)
Noncurrent [Member] | Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	18.0	4.0
Less than 12 Months, Unrealized Losses	(4.3)	(0.7)
12 Months or More, Fair Value	9.6	0.0
12 Months or More, Unrealized Losses	(2.3)	0.0
Total, Fair Value	27.6	4.0
Total, Unrealized Losses	$ (6.6)	$ (0.7)