Fair Value Measurements - Carrying Amounts and Estimated Fair Value for Financial Instrument Assets (Liabilities) (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021
Financial assets:
Interest-bearing deposits at banks	$ 30,114,286		$ 24,958,719
Federal funds sold			3,000
Investment securities	27,336,103		25,210,871
Loans and leases:
Loans and leases	133,133,497		132,074,156
Allowance for credit losses	(2,052,127)	$ (1,998,366)	(1,925,331)	$ (1,875,591)	$ (1,823,790)	$ (1,469,226)
Loans and leases, net	130,302,558		129,638,832
Financial liabilities:
Noninterest-bearing deposits	(53,786,987)		(65,501,860)
Savings and interest-checking deposits	(90,297,219)		(87,911,463)
Time deposits	(20,043,601)		(10,101,545)
Short-term borrowings	(530,663)		(354,670)
Long-term borrowings	(7,123,426)		(3,964,537)
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial assets:
Cash and cash equivalents	1,701,427		1,371,688
Trading account	118,838		117,847
Investment securities	252,080		145,289
Significant Observable Inputs (Level 2) [Member]
Financial assets:
Cash and cash equivalents	67,437		145,556
Interest-bearing deposits at banks	30,114,286		24,958,719
Federal funds sold			3,000
Trading account	18,160
Investment securities	25,231,860		23,860,445
Loans and leases:
Loans and leases, net	7,034,104		7,180,192
Accrued interest receivable	734,036		646,250
Financial liabilities:
Noninterest-bearing deposits	(53,786,987)		(65,501,860)
Savings and interest-checking deposits	(90,297,219)		(87,911,463)
Time deposits	(19,931,959)		(10,143,110)
Short-term borrowings	(6,730,663)		(3,554,951)
Long-term borrowings	(6,811,799)		(3,926,489)
Accrued interest payable	(401,752)		(81,356)
Other financial instruments:
Commitments to sell real estate loans	65,337		54,424
Interest rate swap agreements used for interest rate risk management	12,185		(7,892)
Interest rate and foreign exchange contracts not designated as hedging instruments	(1,095,612)		(920,316)
Significant Unobservable Inputs (Level 3) [Member]
Financial assets:
Investment securities	45,986		50,588
Loans and leases:
Consumer loans	19,351,349		20,093,523
Loans and leases, net	118,417,220		119,048,176
Other financial instruments:
Commitments to originate real estate loans for sale	(51,403)		(45,573)
Other credit-related commitments	(150,708)		(148,772)
Carrying Amount [Member]
Financial assets:
Cash and cash equivalents	1,768,864		1,517,244
Interest-bearing deposits at banks	30,114,286		24,958,719
Federal funds sold			3,000
Trading account	136,998		117,847
Investment securities	27,336,103		25,210,871
Loans and leases:
Consumer loans	20,274,784		20,593,079
Allowance for credit losses	(2,052,127)		(1,925,331)
Loans and leases, net	130,302,558		129,638,832
Accrued interest receivable	734,036		646,250
Financial liabilities:
Noninterest-bearing deposits	(53,786,987)		(65,501,860)
Savings and interest-checking deposits	(90,297,219)		(87,911,463)
Time deposits	(20,043,601)		(10,101,545)
Short-term borrowings	(6,730,663)		(3,554,951)
Long-term borrowings	(7,123,426)		(3,964,537)
Accrued interest payable	(401,752)		(81,356)
Other financial instruments:
Commitments to originate real estate loans for sale	(51,403)		(45,573)
Commitments to sell real estate loans	65,337		54,424
Other credit-related commitments	(150,708)		(148,772)
Interest rate swap agreements used for interest rate risk management	12,185		(7,892)
Interest rate and foreign exchange contracts not designated as hedging instruments	(1,095,612)		(920,316)
Cumulative Amount of Fair Value Hedging Adjustment Increasing (Decreasing) the Carrying Amount [Member]
Financial assets:
Cash and cash equivalents	1,768,864		1,517,244
Interest-bearing deposits at banks	30,114,286		24,958,719
Federal funds sold			3,000
Trading account	136,998		117,847
Investment securities	25,529,926		24,056,322
Loans and leases:
Consumer loans	19,351,349		20,093,523
Loans and leases, net	125,451,324		126,228,368
Accrued interest receivable	734,036		646,250
Financial liabilities:
Noninterest-bearing deposits	(53,786,987)		(65,501,860)
Savings and interest-checking deposits	(90,297,219)		(87,911,463)
Time deposits	(19,931,959)		(10,143,110)
Short-term borrowings	(6,730,663)		(3,554,951)
Long-term borrowings	(6,811,799)		(3,926,489)
Accrued interest payable	(401,752)		(81,356)
Other financial instruments:
Commitments to originate real estate loans for sale	(51,403)		(45,573)
Commitments to sell real estate loans	65,337		54,424
Other credit-related commitments	(150,708)		(148,772)
Interest rate swap agreements used for interest rate risk management	12,185		(7,892)
Interest rate and foreign exchange contracts not designated as hedging instruments	(1,095,612)		(920,316)
Commercial Loans and Leases [Member] | Significant Unobservable Inputs (Level 3) [Member]
Loans and leases:
Loans and leases	44,080,119		41,139,985
Commercial Loans and Leases [Member] | Carrying Amount [Member]
Loans and leases:
Loans and leases	45,058,033		41,850,566
Commercial Loans and Leases [Member] | Cumulative Amount of Fair Value Hedging Adjustment Increasing (Decreasing) the Carrying Amount [Member]
Loans and leases:
Loans and leases	44,080,119		41,139,985
Commercial [Member] | Significant Observable Inputs (Level 2) [Member]
Loans and leases:
Loans and leases	226,022		130,652
Commercial [Member] | Significant Unobservable Inputs (Level 3) [Member]
Loans and leases:
Loans and leases	41,047,058		43,083,994
Commercial [Member] | Carrying Amount [Member]
Loans and leases:
Loans and leases	43,573,598		45,364,571
Commercial [Member] | Cumulative Amount of Fair Value Hedging Adjustment Increasing (Decreasing) the Carrying Amount [Member]
Loans and leases:
Loans and leases	41,273,080		43,214,646
Residential Real Estate Loans | Significant Observable Inputs (Level 2) [Member]
Loans and leases:
Loans and leases	6,808,082		7,049,540
Residential Real Estate Loans | Significant Unobservable Inputs (Level 3) [Member]
Loans and leases:
Loans and leases	13,938,694		14,730,674
Residential Real Estate Loans | Carrying Amount [Member]
Loans and leases:
Loans and leases	23,448,270		23,755,947
Residential Real Estate Loans | Cumulative Amount of Fair Value Hedging Adjustment Increasing (Decreasing) the Carrying Amount [Member]
Loans and leases:
Loans and leases	$ 20,746,776		$ 21,780,214