Credit Quality (Summary of Loans Modified in a TDR) (Detail) $ in Millions		12 Months Ended
		Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	[1],[2]	10,978	14,472	11,102
Recorded Investment in Loans Modified in a TDR During the Period	[2]	$ 413	$ 409	$ 548
Increase (Decrease) to ALLL Upon Modification	[2]	32	23	27
Charge-offs Recognized Upon Modification	[2]	$ 4	$ 10	$ 8
Commercial Portfolio Segment | Commercial and Industrial Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	[1],[2]	74	77	128
Recorded Investment in Loans Modified in a TDR During the Period	[2]	$ 183	$ 146	$ 230
Increase (Decrease) to ALLL Upon Modification	[2]	14	7	12
Charge-offs Recognized Upon Modification	[2]	$ 0	$ 3	$ 6
Commercial Portfolio Segment | Commercial Mortgage Loans, Owner-Occupied
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	[1],[2]	12	18	32
Recorded Investment in Loans Modified in a TDR During the Period	[2]	$ 11	$ 16	$ 54
Increase (Decrease) to ALLL Upon Modification	[2]	0	(2)	(1)
Charge-offs Recognized Upon Modification	[2]	$ 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],[2]	4	12	28
Recorded Investment in Loans Modified in a TDR During the Period	[2]	$ 5	$ 7	$ 30
Increase (Decrease) to ALLL Upon Modification	[2]	2	(1)	(3)
Charge-offs Recognized Upon Modification	[2]	$ 0	$ 0	$ 2
Commercial Portfolio Segment | Commercial Leases
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	[1],[2]	5
Recorded Investment in Loans Modified in a TDR During the Period	[2]	$ 16
Increase (Decrease) to ALLL Upon Modification	[2]	0
Charge-offs Recognized Upon Modification	[2]	$ 0
Residential Mortgage Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	[1],[2]	924	1,089	1,093
Recorded Investment in Loans Modified in a TDR During the Period	[2]	$ 137	$ 155	$ 160
Increase (Decrease) to ALLL Upon Modification	[2]	8	8	8
Charge-offs Recognized Upon Modification	[2]	$ 0	$ 0	$ 0
Consumer Portfolio Segment | Home Equity
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	[1],[2]	219	267	284
Recorded Investment in Loans Modified in a TDR During the Period	[2]	$ 15	$ 16	$ 12
Increase (Decrease) to ALLL Upon Modification	[2]	0	(1)	0
Charge-offs Recognized Upon Modification	[2]	$ 0	$ 0	$ 0
Consumer Portfolio Segment | Automobile Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	[1],[2]	221	440	608
Recorded Investment in Loans Modified in a TDR During the Period	[2]	$ 3	$ 7	$ 10
Increase (Decrease) to ALLL Upon Modification	[2]	0	1	1
Charge-offs Recognized Upon Modification	[2]	$ 0	$ 0	$ 0
Consumer Portfolio Segment | Credit Card
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	[1],[2]	9,519	12,569	8,929
Recorded Investment in Loans Modified in a TDR During the Period	[2]	$ 43	$ 62	$ 52
Increase (Decrease) to ALLL Upon Modification	[2]	8	11	10
Charge-offs Recognized Upon Modification	[2]	$ 4	$ 7	$ 0

[1] Represents number of loans post-modification and excludes loans previously modified in a TDR .

[2] Excludes all loans and leases held for sale and loans acquired with deteriorated credit quality which were accounted for within a pool .