Derivatives (Notional Amounts and Fair Values for All Derivative Instruments Included in the Consolidated Balance Sheets) (Detail) - USD ($) $ in Millions	Dec. 31, 2019		Dec. 31, 2018
Derivatives, Fair Value
Notional Amount	$ 456.5
Derivative Asset, Fair Value, Gross Asset	1,673.0		$ 1,114.0
Derivative Liability, Fair Value, Gross Liability	741.0		874.0
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges
Derivatives, Fair Value
Derivative Asset, Fair Value, Gross Asset	508.0		346.0
Derivative Liability, Fair Value, Gross Liability	2.0		29.0
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Fair Value Hedging
Derivatives, Fair Value
Derivative Asset, Fair Value, Gross Asset	393.0		262.0
Derivative Liability, Fair Value, Gross Liability	0.0		2.0
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Fair Value Hedging | Interest Rate Swap | Long-term debt
Derivatives, Fair Value
Notional Amount	2,705.0		3,455.0
Derivative Asset, Fair Value, Gross Asset	393.0		262.0
Derivative Liability, Fair Value, Gross Liability	0.0		2.0
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Cash Flow Hedging
Derivatives, Fair Value
Derivative Asset, Fair Value, Gross Asset	115.0		84.0
Derivative Liability, Fair Value, Gross Liability	2.0		27.0
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Cash Flow Hedging | Interest Rate Swap | Commercial and Industrial Loans
Derivatives, Fair Value
Notional Amount	8,000.0		8,000.0
Derivative Asset, Fair Value, Gross Asset	0.0		15.0
Derivative Liability, Fair Value, Gross Liability	2.0		27.0
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Cash Flow Hedging | Interest Rate Floor | Commercial and Industrial Loans
Derivatives, Fair Value
Notional Amount	3,000.0		3,000.0
Derivative Asset, Fair Value, Gross Asset	115.0		69.0
Derivative Liability, Fair Value, Gross Liability	0.0		0.0
Nondesignated
Derivatives, Fair Value
Derivative Asset, Fair Value, Gross Asset	1,165.0		768.0
Derivative Liability, Fair Value, Gross Liability	739.0		845.0
Nondesignated | Risk Management And Other Business Purposes
Derivatives, Fair Value
Derivative Asset, Fair Value, Gross Asset	132.0		44.0
Derivative Liability, Fair Value, Gross Liability	175.0		147.0
Nondesignated | Risk Management And Other Business Purposes | Interest Rate Contract | Mortgage Servicing Rights
Derivatives, Fair Value
Notional Amount	6,420.0		10,045.0
Derivative Asset, Fair Value, Gross Asset	131.0		40.0
Derivative Liability, Fair Value, Gross Liability	2.0		14.0
Nondesignated | Risk Management And Other Business Purposes | Forward Contracts Related to Residential Mortgage LoansHeld for Sale | Loans Held For Sale
Derivatives, Fair Value
Notional Amount	2,901.0		926.0
Derivative Asset, Fair Value, Gross Asset	1.0		0.0
Derivative Liability, Fair Value, Gross Liability	5.0		8.0
Nondesignated | Risk Management And Other Business Purposes | Swap
Derivatives, Fair Value
Notional Amount	3,082.0		2,174.0
Derivative Asset, Fair Value, Gross Asset	0.0		0.0
Derivative Liability, Fair Value, Gross Liability	163.0		125.0
Nondesignated | Risk Management And Other Business Purposes | Foreign Exchange Contract
Derivatives, Fair Value
Notional Amount	195.0		133.0
Derivative Asset, Fair Value, Gross Asset	0.0		4.0
Derivative Liability, Fair Value, Gross Liability	5.0		0.0
Nondesignated | Customer Accommodation
Derivatives, Fair Value
Derivative Asset, Fair Value, Gross Asset	1,033.0		724.0
Derivative Liability, Fair Value, Gross Liability	564.0		698.0
Nondesignated | Customer Accommodation | Interest Rate Contract
Derivatives, Fair Value
Notional Amount	73,327.0	[1]	55,012.0
Derivative Asset, Fair Value, Gross Asset	579.0	[1]	262.0
Derivative Liability, Fair Value, Gross Liability	148.0	[1]	278.0
Nondesignated | Customer Accommodation | Interest Rate Lock Commitments
Derivatives, Fair Value
Notional Amount	907.0		407.0
Derivative Asset, Fair Value, Gross Asset	18.0		7.0
Derivative Liability, Fair Value, Gross Liability	0.0		0.0
Nondesignated | Customer Accommodation | Commodity Contract
Derivatives, Fair Value
Notional Amount	8,525.0		6,511.0
Derivative Asset, Fair Value, Gross Asset	271.0		307.0
Derivative Liability, Fair Value, Gross Liability	270.0		278.0
Nondesignated | Customer Accommodation | TBA Securities
Derivatives, Fair Value
Notional Amount	50.0		18.0
Derivative Asset, Fair Value, Gross Asset	0.0		0.0
Derivative Liability, Fair Value, Gross Liability	0.0		0.0
Nondesignated | Customer Accommodation | Foreign Exchange Contract
Derivatives, Fair Value
Notional Amount	14,144.0		13,205.0
Derivative Asset, Fair Value, Gross Asset	165.0		148.0
Derivative Liability, Fair Value, Gross Liability	$ 146.0		$ 142.0

[1] Derivative assets and liabilities are presented net of variation margin of $40 and $493, respectively.