Share-Based Payments (Details 9) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Shares issued under ESPP	6,200,000
2015 ESPP
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Shares issued under ESPP	167,000	190,000	78,000
Cash received under ESPP	$ 39.8	$ 41.5	$ 19.3
1995 ESPP
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Shares issued under ESPP	0	0	98,000
Cash received under ESPP	$ 0.0	$ 0.0	$ 30.0