Loans and Allowance for Loan Losses - Reconciliation of Changes in Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	$ 513	$ 748	$ 639	$ 723
(Reversal of) provision for loan losses	33	68	(1)	190
Other	2	(1)	2	3
Loans charged-off	(17)	(128)	(123)	(236)
Recoveries of loans previously charged-off	11	4	25	11
Allowance for loan losses, end of period	542	691	542	691
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	435	683	556	653
(Reversal of) provision for loan losses	(7)	55	(57)	180
Other	2	(1)	2	3
Loans charged-off	(7)	(126)	(91)	(231)
Recoveries of loans previously charged-off	8	3	21	9
Allowance for loan losses, end of period	431	614	431	614
Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	78	65	83	50
(Reversal of) provision for loan losses	10	13	26	30
Other	0	0	0	0
Loans charged-off	(10)	(2)	(32)	(5)
Recoveries of loans previously charged-off	3	1	4	2
Allowance for loan losses, end of period	81	77	81	77
Unallocated
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	0	0	0	20
(Reversal of) provision for loan losses	30	0	30	(20)
Other	0	0	0	0
Loans charged-off	0	0	0	0
Recoveries of loans previously charged-off	0	0	0	0
Allowance for loan losses, end of period	$ 30	$ 0	$ 30	$ 0

Represents the amount of other allowance for credit losses related to financing receivable.

No definition available.

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

Amount of recovery of financing receivables doubtful of collection that were previously charged off.

+ References

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- Definition

Amount of direct write-downs of financing receivables charged against the allowance.

+ References

+ Details

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- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ 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 (g)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953423-111524

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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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- Definition

Amount of expense related to estimated loss from loan and lease transactions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
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