Goodwill and Mortgage Servicing Rights (Goodwill by Business Segment 10-K) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Line Items]
Goodwill	$ 9,173	$ 9,103	$ 9,103
Retail Banking
Goodwill [Line Items]
Goodwill	5,795	5,795	5,795
Corporate & Institutional Banking
Goodwill [Line Items]
Goodwill	3,314	3,244	3,244
Goodwill from business acquisitions	70
Asset Management Group
Goodwill [Line Items]
Goodwill	$ 64	$ 64	$ 64

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant