Loans - 90+ Day Delinquent Loans Accruing Interest and Nonperforming Loans (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days Past Due and Accruing	$ 2,233	$ 1,936
Nonperforming Loans	$ 899	$ 1,599
Percent 90 days past due and still accruing	0.88%	0.79%
Financing Receivable, Nonaccrual, Percent Past Due	0.35%	0.65%
Credit Card Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days Past Due and Accruing	$ 2,221	$ 1,936
Nonperforming Loans	24	42
Credit Card Portfolio Segment [Member] \| Geographic Distribution, Domestic [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days Past Due and Accruing	2,093	1,840
Credit Card Portfolio Segment [Member] \| Geographic Distribution, Foreign [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days Past Due and Accruing	128	96
Nonperforming Loans	24	42
Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days Past Due and Accruing	0	0
Nonperforming Loans	$ 587	$ 527
Financing Receivable, Nonaccrual, Percent Past Due	0.78%	0.72%
Consumer Portfolio Segment [Member] \| Auto
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days Past Due and Accruing	$ 0	$ 0
Nonperforming Loans	$ 376	$ 223
Financing Receivable, Nonaccrual, Percent Past Due	0.70%	0.47%
Consumer Portfolio Segment [Member] \| Home loan
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days Past Due and Accruing	$ 0	$ 0
Nonperforming Loans	$ 176	$ 273
Financing Receivable, Nonaccrual, Percent Past Due	1.00%	1.26%
Consumer Portfolio Segment [Member] \| Retail banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days Past Due and Accruing	$ 0	$ 0
Nonperforming Loans	$ 35	$ 31
Financing Receivable, Nonaccrual, Percent Past Due	1.00%	0.86%
Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days Past Due and Accruing	$ 12	$ 0
Nonperforming Loans		1,022
Commercial Banking \| Total commercial lending
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days Past Due and Accruing	12	0
Nonperforming Loans	277	1,018
Commercial Banking \| Commercial and multifamily real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days Past Due and Accruing	12	0
Nonperforming Loans	38	30
Commercial Banking \| Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days Past Due and Accruing	0	0
Nonperforming Loans	239	988
Commercial Banking \| Small-ticket commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days Past Due and Accruing	0	0
Nonperforming Loans	7	4
Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days Past Due and Accruing	0	0
Nonperforming Loans	$ 4	$ 8

Financing Receivable, Percent 90 Days Past Due and Still Accruing

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- Definition

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+ References

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- Definition

Recorded investment in financing receivables that are 90 days or more past due and still accruing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5111-111524

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- Definition

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5111-111524

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