Other Assets - Affordable Housing and Other Tax Credit Investment Partnerships (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Provision for income taxes
Affordable housing and other tax credit investment partnership interests
Amortization	$ 3.5	$ 3.3	$ 3.1
Other assets
Affordable housing and other tax credit investment partnership interests
Investment partnership interest	$ 12.9	$ 16.0

Amount of amortization expense of investment in qualified affordable housing projects.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 740
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=64813897&loc=SL49122993-202985

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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