Stock Compensation Plans (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Stock or Unit Expense	$ 21.0	$ 16.0	$ 39.0	$ 29.0
Employee Stock Ownership Plan (ESOP), Compensation Expense	1.0	0.0	2.0	0.0
Allocated Share-based Compensation Expense	22.0	16.0	41.0	29.0
Tax benefit	(6.0)	(4.0)	(12.0)	(8.0)
Total stock-based compensation (net of tax)	$ 16.0	$ 12.0	$ 29.0	$ 21.0
Stock Issued During Period, Shares, Employee Stock Ownership Plan	0.1		0.2
Stock Issued During Period, Price Per Share, Employee Stock Purchase Plans	$ 38.83
Total intrinsic value of shares purchased	$ 0.6		$ 1.5
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation cost related to unvested awards	$ 163.0		$ 163.0
Total unrecognized compensation cost related to unvested awards, period for recognition (in years)			1 year 2 months

Stock Issued During Period, Price Per Share, Employee Stock Purchase Plans

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Total intrinsic value of shares purchased

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- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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The amount of expense, net of income tax, recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Unrecognized cost of unvested share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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The amount of plan compensation cost recognized during the period.

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The noncash expense that represents the cost of restricted stock or unit distributed to employees as compensation.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Number of shares issued during the period as a result of an employee stock purchase plan.

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