Derivatives (Notional Amounts and Fair Values for All Derivative Instruments Included in the Consolidated Balance Sheets) (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value
Fair value - Derivative Assets	$ 865	$ 823
Fair value - Derivative Liabilities	774	602
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges
Derivatives, Fair Value
Fair value - Derivative Assets	248	297
Fair value - Derivative Liabilities	22	17
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Fair Value Hedging
Derivatives, Fair Value
Fair value - Derivative Assets	248	297
Fair value - Derivative Liabilities	4	5
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Fair Value Hedging | Interest Rate Swap | Long-Term Debt
Derivatives, Fair Value
Notional amount	3,705	3,705
Fair value - Derivative Assets	248	297
Fair value - Derivative Liabilities	4	5
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Cash Flow Hedging
Derivatives, Fair Value
Fair value - Derivative Assets	0	0
Fair value - Derivative Liabilities	18	12
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Cash Flow Hedging | Interest Rate Swap | Commercial and Industrial Loans
Derivatives, Fair Value
Notional amount	4,150	4,475
Fair value - Derivative Assets	0	0
Fair value - Derivative Liabilities	18	12
Nondesignated
Derivatives, Fair Value
Fair value - Derivative Assets	617	526
Fair value - Derivative Liabilities	752	585
Nondesignated | Risk Management and Other Business Purposes
Derivatives, Fair Value
Fair value - Derivative Assets	55	75
Fair value - Derivative Liabilities	187	154
Nondesignated | Risk Management and Other Business Purposes | Interest Rate Contract | Servicing Rights
Derivatives, Fair Value
Notional amount	12,135	11,035
Fair value - Derivative Assets	53	54
Fair value - Derivative Liabilities	20	15
Nondesignated | Risk Management and Other Business Purposes | Forward Contracts | Assets Held For Sale
Derivatives, Fair Value
Notional amount	1,153	1,284
Fair value - Derivative Assets	2	1
Fair value - Derivative Liabilities	2	1
Nondesignated | Risk Management and Other Business Purposes | Warrant
Derivatives, Fair Value
Notional amount		20
Fair value - Derivative Assets		20
Fair value - Derivative Liabilities		0
Nondesignated | Risk Management and Other Business Purposes | Swap
Derivatives, Fair Value
Notional amount	1,993	1,900
Fair value - Derivative Assets	0	0
Fair value - Derivative Liabilities	165	137
Nondesignated | Risk Management and Other Business Purposes | Foreign Exchange Contract
Derivatives, Fair Value
Notional amount	138	112
Fair value - Derivative Assets	0	0
Fair value - Derivative Liabilities	0	1
Nondesignated | Customer Accommodation
Derivatives, Fair Value
Fair value - Derivative Assets	562	451
Fair value - Derivative Liabilities	565	431
Nondesignated | Customer Accommodation | Interest Rate Contract
Derivatives, Fair Value
Notional amount	44,973	42,216
Fair value - Derivative Assets	220	154
Fair value - Derivative Liabilities	241	145
Nondesignated | Customer Accommodation | Interest Rate Lock Commitments
Derivatives, Fair Value
Notional amount	667	446
Fair value - Derivative Assets	11	8
Fair value - Derivative Liabilities	0	0
Nondesignated | Customer Accommodation | Commodity Contract
Derivatives, Fair Value
Notional amount	4,843	4,125
Fair value - Derivative Assets	199	165
Fair value - Derivative Liabilities	195	167
Nondesignated | Customer Accommodation | TBAs
Derivatives, Fair Value
Notional amount	46	26
Fair value - Derivative Assets	0	0
Fair value - Derivative Liabilities	0	0
Nondesignated | Customer Accommodation | Foreign Exchange Contract
Derivatives, Fair Value
Notional amount	11,723	12,654
Fair value - Derivative Assets	132	124
Fair value - Derivative Liabilities	$ 129	$ 119