CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (Parenthetical) - $ / shares	9 Months Ended	12 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Statement Of Stockholders Equity [Abstract]
Dividends declared per common share	$ 1.30	$ 2.275
Dividends paid per common share	1.30	2.275
Dividends declared per preferred share	1.3125	1.113
Dividends paid per preferred share	$ 1.3125	$ 1.113

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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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