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, 2016	Dec. 31, 2015
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment	$ 353	$ 529
Post-Modification Outstanding Recorded Investment	352	529
Commercial
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment	337	504
Post-Modification Outstanding Recorded Investment	336	504
Commercial \| Commercial and industrial
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment	327	495
Post-Modification Outstanding Recorded Investment	326	495
Commercial \| Commercial mortgage
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment	10	9
Post-Modification Outstanding Recorded Investment	10	9
Consumer
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment	16	25
Post-Modification Outstanding Recorded Investment	16	25
Consumer \| Residential mortgage
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment	11	18
Post-Modification Outstanding Recorded Investment	11	18
Consumer \| Home equity and other consumer loans
Pre- and Post - modification recorded investments
Pre-Modification Outstanding Recorded Investment	5	7
Post-Modification Outstanding Recorded Investment	$ 5	$ 7

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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=49124121&loc=SL6953676-111524

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

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