Credit Quality (Summary of Loans Modified in a TDR) (Detail) $ in Millions	12 Months Ended
Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	7,056	8,869	9,256
Recorded Investment in Loans Modified in a TDR During the Period	$ 374	$ 415	$ 413
Increase (Decrease) to ALLL Upon Modification	(10)	13	13
Charge-offs Recognized Upon Modification	$ 8	$ 9	$ 7
Commercial Portfolio Segment \| Commercial and Industrial Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	97	54	75
Recorded Investment in Loans Modified in a TDR During the Period	$ 223	$ 200	$ 237
Increase (Decrease) to ALLL Upon Modification	(19)	1	(5)
Charge-offs Recognized Upon Modification	$ 5	$ 7	$ 6
Commercial Portfolio Segment \| Commercial Mortgage Loans, Owner-Occupied
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	15	6	9
Recorded Investment in Loans Modified in a TDR During the Period	$ 12	$ 3	$ 8
Increase (Decrease) to ALLL Upon Modification	0	(1)	5
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 0
Commercial Portfolio Segment \| Commercial Mortgage Loans, Nonowner-Occupied
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	1	3	4
Recorded Investment in Loans Modified in a TDR During the Period	$ 0	$ 0	$ 0
Increase (Decrease) to ALLL Upon Modification	0	0	0
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 0
Commercial Portfolio Segment \| Commercial Leases
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period			1
Recorded Investment in Loans Modified in a TDR During the Period			$ 4
Increase (Decrease) to ALLL Upon Modification			0
Charge-offs Recognized Upon Modification			$ 0
Residential Mortgage Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	722	1,128	830
Recorded Investment in Loans Modified in a TDR During the Period	$ 101	$ 168	$ 116
Increase (Decrease) to ALLL Upon Modification	1	4	5
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 0
Consumer Portfolio Segment \| Home Equity
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	80	111	150
Recorded Investment in Loans Modified in a TDR During the Period	$ 4	$ 7	$ 10
Increase (Decrease) to ALLL Upon Modification	0	0	0
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 0
Consumer Portfolio Segment \| Indirect secured consumer loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	100	84	102
Recorded Investment in Loans Modified in a TDR During the Period	$ 0	$ 0	$ 0
Increase (Decrease) to ALLL Upon Modification	0	0	0
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 0
Consumer Portfolio Segment \| Credit Card
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	6,041	7,483	8,085
Recorded Investment in Loans Modified in a TDR During the Period	$ 34	$ 37	$ 38
Increase (Decrease) to ALLL Upon Modification	8	9	8
Charge-offs Recognized Upon Modification	$ 3	$ 2	$ 1

Amount of other addition (reduction) in allowance reserve for credit loss.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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