Business Combination - Schedule of Operations Included in Consolidated Statement of Income and Unaudited Pro Forma Information (Details) - First Niagara Bank, N.A. [Member] $ in Millions	9 Months Ended
Sep. 30, 2016 USD ($)
Business Acquisition, Pro Forma Information [Abstract]
Net interest income (TE)	$ 2,674
Noninterest income	1,625
Net income (loss) attributable to common shareholders	$ 849

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

Name:	us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration