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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		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 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)	1.6	0.9	2.1	0.9
Aggregate purchase price	$ 73.4	$ 34.9	$ 100.0	$ 34.9
Average purchase price per share (in dollars per share)	$ 47.30	$ 39.92	$ 47.58	$ 39.92
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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6405813&loc=d3e23239-112655

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Publisher FASB
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-Topic 505
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21463-112644

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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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21463-112644

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