Shareholders' Equity (Summary of Dividends) (Details) - $ / shares	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016
Dividends [Abstract]
Dividends declared per common share	$ 2.96	$ 2.860
Dividends paid per common share	2.94	2.820
Dividends declared per preferred share	1.016	1.016
Dividends paid per preferred share	$ 1.016	$ 1.016

Aggregate dividends paid during the period for each share of common stock outstanding.

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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Aggregate dividends declared during the period for each share of common stock outstanding.

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Aggregate dividends paid during the period for each share of preferred stock outstanding.

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Aggregate dividends declared during the period for each share of preferred stock outstanding.

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