Credit Quality (Summary of Subsequent Defaults) (Detail) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)
Financing Receivable, Modifications
Number of contracts	[1]	505	175	1,378	1,410
Recorded Investment in Loans Modified in a TDR During the Period	[1]	$ 10	$ 5	$ 29	$ 28
Commercial Portfolio Segment | Commercial and Industrial Loans
Financing Receivable, Modifications
Number of contracts	[1]	1	0	4	4
Recorded Investment in Loans Modified in a TDR During the Period	[1]	$ 1	$ 0	$ 4	$ 7
Commercial Portfolio Segment | Commercial Mortgage Loans, Nonowner-Occupied
Financing Receivable, Modifications
Number of contracts	[1]	0	0	2	0
Recorded Investment in Loans Modified in a TDR During the Period	[1]	$ 0	$ 0	$ 0	$ 0
Commercial Portfolio Segment | Commercial Leases
Financing Receivable, Modifications
Number of contracts	[1]	2	0	2	0
Recorded Investment in Loans Modified in a TDR During the Period	[1]	$ 1	$ 0	$ 1	$ 0
Residential Mortgage Loans
Financing Receivable, Modifications
Number of contracts	[1]	41	31	127	101
Recorded Investment in Loans Modified in a TDR During the Period	[1]	$ 6	$ 5	$ 18	$ 14
Consumer Portfolio Segment | Home Equity
Financing Receivable, Modifications
Number of contracts	[1]	3	4	11	12
Recorded Investment in Loans Modified in a TDR During the Period	[1]	$ 0	$ 0	$ 1	$ 1
Consumer Portfolio Segment | Automobile Loans
Financing Receivable, Modifications
Number of contracts	[1]	0	0	0	8
Recorded Investment in Loans Modified in a TDR During the Period	[1]	$ 0	$ 0	$ 0	$ 0
Consumer Portfolio Segment | Credit Card
Financing Receivable, Modifications
Number of contracts	[1]	458	140	1,232	1,285
Recorded Investment in Loans Modified in a TDR During the Period	[1]	$ 2	$ 0	$ 5	$ 6

[1] (a) Excludes all loans and leases held for sale and loans acquired with deteriorated credit quality.