Loans and Allowance for Loan Losses - Reconciliation of Changes in Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	$ 474	$ 476
(Reversal of) provision for loan losses	59	(5)
Loans charged-off	(28)	(16)
Recoveries of loans previously charged-off	11	5
Allowance for loan losses, end of period	516	460
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	359	360
(Reversal of) provision for loan losses	32	14
Recoveries of loans previously charged-off		3
Allowance for loan losses, end of period	389	371
Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	110	86
(Reversal of) provision for loan losses	27	6
Recoveries of loans previously charged-off		2
Allowance for loan losses, end of period	122	84
Unallocated
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period		30
(Reversal of) provision for loan losses	0	(25)
Loans charged-off	0	0
Recoveries of loans previously charged-off	0	0
Allowance for loan losses, end of period	5	5
Commercial Loans
Allowance for Loan and Lease Losses [Roll Forward]
Loans charged-off	(11)	(6)
Recoveries of loans previously charged-off	9
Commercial Loans \| Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	359
Consumer Loans
Allowance for Loan and Lease Losses [Roll Forward]
Loans charged-off	(17)	$ (10)
Recoveries of loans previously charged-off	2
Consumer Loans \| Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	$ 110

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

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.

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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=84173941&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

Reference 4: http://www.xbrl.org/2003/role/presentationRef
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-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=82894903&loc=d3e15032-111544

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- Definition

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

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
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-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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