Credit Quality (Summary of Subsequent Defaults) (Detail) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)		Sep. 30, 2018 USD ($)		Sep. 30, 2017 USD ($)
Financing Receivable, Modifications
Number of contracts		183	472		679		1,410
Recorded Investment in Loans Modified in a TDR During the Period		$ 37	$ 10		$ 88		$ 45
Commercial Portfolio Segment | Commercial and Industrial Loans
Financing Receivable, Modifications
Number of contracts	[1]	5	3		8		7
Recorded Investment in Loans Modified in a TDR During the Period	[1]	$ 32	$ 1		$ 61		$ 17
Commercial Portfolio Segment | Commercial Mortgage Loans, Owner-occupied
Financing Receivable, Modifications
Number of contracts			1		2	[1]	4
Recorded Investment in Loans Modified in a TDR During the Period			$ 0		$ 0	[1]	$ 1
Residential Mortgage Loans
Financing Receivable, Modifications
Number of contracts		28	49		138		132
Recorded Investment in Loans Modified in a TDR During the Period		$ 4	$ 7		$ 24		$ 19
Consumer Portfolio Segment | Home Equity
Financing Receivable, Modifications
Number of contracts		4	2	[1]	6	[1]	13	[1]
Recorded Investment in Loans Modified in a TDR During the Period		$ 0	$ 0	[1]	$ 0	[1]	$ 2	[1]
Consumer Portfolio Segment | Credit Card
Financing Receivable, Modifications
Number of contracts	[1]	146	417		525		1,254
Recorded Investment in Loans Modified in a TDR During the Period	[1]	$ 1	$ 2		$ 3		$ 6

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