Loans and Allowance for Loan Losses - Pre and Post Modification Outstanding Recorded Investment Amounts of TDRs (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment	$ 180	$ 362
Post-Modification Outstanding Recorded Investment	180	341
Commercial
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment	169	343
Post-Modification Outstanding Recorded Investment	169	322
Commercial \| Commercial and industrial
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment		186
Post-Modification Outstanding Recorded Investment		186
Commercial \| Commercial mortgage
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment	4	5
Post-Modification Outstanding Recorded Investment	4	5
Commercial \| Construction
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment	0	152
Post-Modification Outstanding Recorded Investment	0	131
Consumer
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment	11	19
Post-Modification Outstanding Recorded Investment	11	19
Consumer \| Residential mortgage
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment		16
Post-Modification Outstanding Recorded Investment		16
Consumer \| Home equity and other consumer loans
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment	2	3
Post-Modification Outstanding Recorded Investment	2	$ 3
Commercial Portfolio Segment [Member] \| Commercial and industrial
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment	165
Post-Modification Outstanding Recorded Investment	165
Consumer Portfolio Segment [Member] \| Residential mortgage
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment	9
Post-Modification Outstanding Recorded Investment	$ 9

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Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953676-111524

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Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

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