Presentation of Financial Statements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Changes [Line Items]
Income tax benefit	$ (696.2)	$ (600.5)	$ (583.6)
Cumulative effect of accounting changes		(27.1)
Accounting Standards Update 2016-09 [Member]
Accounting Changes [Line Items]
Income tax benefit	$ 20.8
Excess tax benefit from share-based compensation, operating activities		(21.2)	(27.2)
Excess tax benefit from share-based compensation, financing activities		21.2	$ 27.2
Additional Paid-in Capital
Accounting Changes [Line Items]
Cumulative effect of accounting changes		4.5
Additional Paid-in Capital | Accounting Standards Update 2016-09 [Member]
Accounting Changes [Line Items]
Cumulative effect of accounting changes		4.5
Retained Earnings
Accounting Changes [Line Items]
Cumulative effect of accounting changes		(31.6)
Retained Earnings | Accounting Standards Update 2016-09 [Member]
Accounting Changes [Line Items]
Cumulative effect of accounting changes		(4.5)
Retained Earnings | Accounting Standards Update 2016-16 [Member]
Accounting Changes [Line Items]
Cumulative effect of accounting changes		$ (27.1)