Credit Quality (Summary of Subsequent Defaults) (Detail) $ in Millions	12 Months Ended
Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Financing Receivable, Modifications
Number of contracts	961	900	1,832
Recorded Investment in Loans Modified in a TDR During the Period	$ 66	$ 100	$ 52
Commercial Portfolio Segment \| Commercial and Industrial Loans
Financing Receivable, Modifications
Number of contracts	12	8	7
Recorded Investment in Loans Modified in a TDR During the Period	$ 20	$ 61	$ 17
Commercial Portfolio Segment \| Commercial Mortgage Loans, Owner-Occupied
Financing Receivable, Modifications
Number of contracts	4	2	4
Recorded Investment in Loans Modified in a TDR During the Period	$ 1	$ 0	$ 1
Commercial Portfolio Segment \| Commercial Mortgage Loans, Nonowner-Occupied
Financing Receivable, Modifications
Number of contracts	1
Recorded Investment in Loans Modified in a TDR During the Period	$ 0
Residential Mortgage Loans
Financing Receivable, Modifications
Number of contracts	274	225	172
Recorded Investment in Loans Modified in a TDR During the Period	$ 42	$ 35	$ 24
Consumer Portfolio Segment \| Home Equity
Financing Receivable, Modifications
Number of contracts	15	10	16
Recorded Investment in Loans Modified in a TDR During the Period	$ 0	$ 0	$ 2
Consumer Portfolio Segment \| Credit Card
Financing Receivable, Modifications
Number of contracts	655	655	1,633
Recorded Investment in Loans Modified in a TDR During the Period	$ 3	$ 4	$ 8

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Number of financing receivable contracts modified as troubled debt restructuring within previous 12 months, with subsequent payment default.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953682-111524

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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953682-111524

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