Business Combination - Schedule of Operations Included in Consolidated Statement of Income and Unaudited Pro Forma Information (Details) - First Niagara Bank, N.A. [Member] - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net interest income (TE)	$ 3,599	$ 3,564
Noninterest income	2,231	2,206
Net income (loss) attributable to common shareholders	$ 1,161	$ 1,187

The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(2)-(3)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration