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Shareholders' Equity (Shares Repurchased Under Share Repurchase Program) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Class of Stock [Line Items]
Aggregate purchase price			$ 100.0
Stock Repurchase Program Board Authorized Repurchases [Member]
Class of Stock [Line Items]
Shares repurchased (in shares)	0.0	9.2	2.1	10.1
Aggregate purchase price	$ 0.0	$ 400.0	$ 100.0	$ 434.9
Average purchase price per share (in dollars per share)	$ 0	$ 43.28	$ 47.58	$ 42.99
Remaining amount available for share repurchase	$ 263.7		$ 263.7

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Amount remaining of a stock repurchase plan authorized.

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Total cost of shares repurchased divided by the total number of shares repurchased.

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Number of shares that have been repurchased during the period and are being held in treasury.

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Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method.

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