Presentation of Financial Statements (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Accounting Changes [Line Items]
Revenue	$ 3,629.6	$ 3,587.4
Operating Expenses	3,207.9	3,171.7
Operating Income (Loss)	421.7	415.7
Interest Expense	62.3	59.3
Accounting Standards Update 2017-07 [Member]
Accounting Changes [Line Items]
Interest Expense	6.2	$ 5.8
Retained Earnings [Member] | Accounting Standards Update 2014-09 [Member]
Accounting Changes [Line Items]
Cumulative effect adjustment			$ 19.5
Retained Earnings [Member] | Accounting Standards Update 2016-01 [Member]
Accounting Changes [Line Items]
Cumulative effect adjustment			$ 4.1
Adjustments
Accounting Changes [Line Items]
Revenue	42.5
Operating Expenses	36.0
Operating Income (Loss)	6.5
Amounts without the Adoption of ASC 606
Accounting Changes [Line Items]
Revenue	3,672.1
Operating Expenses	3,243.9
Operating Income (Loss)	$ 428.2