Fair Value (Available-For-Sale Securities) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Fair Value Disclosure [Line Items]
Amortized Cost	$ 126.4	$ 129.4
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	3.1	0.4
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(0.1)	(1.1)
Fair Value	129.4	128.7
Government
Fair Value Disclosure [Line Items]
Amortized Cost	37.1	33.7
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	1.2	0.1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0.0	(0.3)
Fair Value	38.3	33.5
Corporate Debt Securities
Fair Value Disclosure [Line Items]
Amortized Cost	89.3	95.7
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	1.9	0.3
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(0.1)	(0.8)
Fair Value	$ 91.1	$ 95.2