Loans and Allowance for Loan Losses - Average Recorded Investment in Impaired Loans (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Loan impairment
Average Recorded Investment	$ 595	$ 563	$ 623
Recognized Interest Income	18	19	37
Commercial portfolio
Loan impairment
Average Recorded Investment	269	224	304
Recognized Interest Income	7	7	26
Allowance for loan losses:
Transfer of loans from held for investment to held for sale	397	203
Loans receivable sold during the period	380	196
Commercial portfolio \| Commercial and industrial
Loan impairment
Average Recorded Investment	241	188	243
Recognized Interest Income	6	5	14
Commercial portfolio \| Commercial mortgage
Loan impairment
Average Recorded Investment	28	36	53
Recognized Interest Income	1	2	9
Commercial portfolio \| Construction
Loan impairment
Average Recorded Investment	0	0	8
Recognized Interest Income	0	0	3
Consumer portfolio
Loan impairment
Average Recorded Investment	324	337	315
Recognized Interest Income	11	12	11
Allowance for loan losses:
Transfer of loans from held for investment to held for sale	810
Consumer portfolio \| Residential mortgage
Loan impairment
Average Recorded Investment	294	310	293
Recognized Interest Income	9	10	10
Consumer portfolio \| Home equity and other consumer loans
Loan impairment
Average Recorded Investment	30	27	22
Recognized Interest Income	2	2	1
Total, excluding purchased credit impaired loans
Loan impairment
Average Recorded Investment	593	561	619
Recognized Interest Income	18	19	37
Purchased credit-impaired loans
Loan impairment
Average Recorded Investment	2	2	4
Recognized Interest Income	$ 0	$ 0	$ 0

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No definition available.

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The amount of financing receivables reclassified to held for sale during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524

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The amount of any significant sales of financing receivables during the reporting period.

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Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5258-111524

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Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

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