Derivatives (Notional Amounts and Fair Values for All Derivative Instruments Included in the Consolidated Balance Sheets) (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value
Fair value - Derivative Assets	$ 945	$ 823
Fair value - Derivative Liabilities	859	602
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges
Derivatives, Fair Value
Fair value - Derivative Assets	230	297
Fair value - Derivative Liabilities	19	17
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Fair Value Hedging
Derivatives, Fair Value
Fair value - Derivative Assets	229	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	3,205	3,705
Fair value - Derivative Assets	229	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	1	0
Fair value - Derivative Liabilities	15	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	6,150	4,475
Fair value - Derivative Assets	1	0
Fair value - Derivative Liabilities	15	12
Nondesignated
Derivatives, Fair Value
Fair value - Derivative Assets	715	526
Fair value - Derivative Liabilities	840	585
Nondesignated | Risk Management and Other Business Purposes
Derivatives, Fair Value
Fair value - Derivative Assets	54	75
Fair value - Derivative Liabilities	181	154
Nondesignated | Risk Management and Other Business Purposes | Interest Rate Contract | Servicing Rights
Derivatives, Fair Value
Notional amount	11,475	11,035
Fair value - Derivative Assets	52	54
Fair value - Derivative Liabilities	13	15
Nondesignated | Risk Management and Other Business Purposes | Forward Contracts | Assets Held For Sale
Derivatives, Fair Value
Notional amount	1,450	1,284
Fair value - Derivative Assets	0	1
Fair value - Derivative Liabilities	4	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	2,207	1,900
Fair value - Derivative Assets	0	0
Fair value - Derivative Liabilities	164	137
Nondesignated | Risk Management and Other Business Purposes | Foreign Exchange Contract
Derivatives, Fair Value
Notional amount	153	112
Fair value - Derivative Assets	2	0
Fair value - Derivative Liabilities	0	1
Nondesignated | Customer Accommodation
Derivatives, Fair Value
Fair value - Derivative Assets	661	451
Fair value - Derivative Liabilities	659	431
Nondesignated | Customer Accommodation | Interest Rate Contract
Derivatives, Fair Value
Notional amount	48,949	42,216
Fair value - Derivative Assets	247	154
Fair value - Derivative Liabilities	280	145
Nondesignated | Customer Accommodation | Interest Rate Lock Commitments
Derivatives, Fair Value
Notional amount	596	446
Fair value - Derivative Assets	11	8
Fair value - Derivative Liabilities	0	0
Nondesignated | Customer Accommodation | Commodity Contract
Derivatives, Fair Value
Notional amount	5,087	4,125
Fair value - Derivative Assets	284	165
Fair value - Derivative Liabilities	270	167
Nondesignated | Customer Accommodation | TBAs
Derivatives, Fair Value
Notional amount	58	26
Fair value - Derivative Assets	0	0
Fair value - Derivative Liabilities	0	0
Nondesignated | Customer Accommodation | Foreign Exchange Contract
Derivatives, Fair Value
Notional amount	10,842	12,654
Fair value - Derivative Assets	119	124
Fair value - Derivative Liabilities	$ 109	$ 119