Fair Value Measurements - Carrying Amounts and Estimated Fair Value for Financial Instrument Assets (Liabilities) (Detail) - USD ($) $ in Thousands	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021
Financial assets:
Interest-bearing deposits at banks	$ 27,106,899		$ 24,958,719
Federal funds sold			3,000
Investment securities	27,916,455		25,210,871
Loans and leases:
Loans and leases	134,061,568		132,074,156
Allowance for credit losses	(1,998,366)	$ (1,975,110)	(1,925,331)	$ (1,823,790)	$ (1,472,359)	$ (1,469,226)
Loans and leases, net	131,345,363		129,638,832
Financial liabilities:
Noninterest-bearing deposits	(54,937,913)		(65,501,860)
Savings and interest-checking deposits	(88,046,247)		(87,911,463)
Time deposits	(19,074,220)		(10,101,545)
Long-term borrowings	(7,416,638)		(3,964,537)
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial assets:
Cash and cash equivalents	1,780,005		1,371,688
Trading account	137,240		117,847
Investment securities	211,341		145,289
Significant Observable Inputs (Level 2) [Member]
Financial assets:
Cash and cash equivalents	68,381		145,556
Interest-bearing deposits at banks	27,106,899		24,958,719
Federal funds sold			3,000
Investment securities	26,451,387		23,860,445
Loans and leases:
Loans and leases, net	7,578,943		7,180,192
Accrued interest receivable	695,030		646,250
Financial liabilities:
Noninterest-bearing deposits	(54,937,913)		(65,501,860)
Savings and interest-checking deposits	(88,046,247)		(87,911,463)
Time deposits	(18,968,171)		(10,143,110)
Short-term borrowings	(7,907,884)		(3,554,951)
Long-term borrowings	(7,091,668)		(3,926,489)
Accrued interest payable	(389,251)		(81,356)
Other financial instruments:
Commitments to sell real estate loans	54,533		54,424
Interest rate swap agreements used for interest rate risk management	2,133		(7,892)
Interest rate and foreign exchange contracts not designated as hedging instruments	(940,230)		(920,316)
Significant Unobservable Inputs (Level 3) [Member]
Financial assets:
Investment securities	49,117		50,588
Loans and leases:
Consumer loans	19,335,779		20,093,523
Loans and leases, net	119,761,668		119,048,176
Other financial instruments:
Commitments to originate real estate loans for sale	(37,178)		(45,573)
Other credit-related commitments	(155,903)		(148,772)
Carrying Amount [Member]
Financial assets:
Cash and cash equivalents	1,848,386		1,517,244
Interest-bearing deposits at banks	27,106,899		24,958,719
Federal funds sold			3,000
Trading account	137,240		117,847
Investment securities	27,916,455		25,210,871
Loans and leases:
Consumer loans	20,249,252		20,593,079
Allowance for credit losses	(1,998,366)		(1,925,331)
Loans and leases, net	131,345,363		129,638,832
Accrued interest receivable	695,030		646,250
Financial liabilities:
Noninterest-bearing deposits	(54,937,913)		(65,501,860)
Savings and interest-checking deposits	(88,046,247)		(87,911,463)
Time deposits	(19,074,220)		(10,101,545)
Short-term borrowings	(7,907,884)		(3,554,951)
Long-term borrowings	(7,416,638)		(3,964,537)
Accrued interest payable	(389,251)		(81,356)
Other financial instruments:
Commitments to originate real estate loans for sale	(37,178)		(45,573)
Commitments to sell real estate loans	54,533		54,424
Other credit-related commitments	(155,903)		(148,772)
Interest rate swap agreements used for interest rate risk management	2,133		(7,892)
Interest rate and foreign exchange contracts not designated as hedging instruments	(940,230)		(920,316)
Cumulative Amount of Fair Value Hedging Adjustment Increasing (Decreasing) the Carrying Amount [Member]
Financial assets:
Cash and cash equivalents	1,848,386		1,517,244
Interest-bearing deposits at banks	27,106,899		24,958,719
Federal funds sold			3,000
Trading account	137,240		117,847
Investment securities	26,711,845		24,056,322
Loans and leases:
Consumer loans	19,335,779		20,093,523
Loans and leases, net	127,340,611		126,228,368
Accrued interest receivable	695,030		646,250
Financial liabilities:
Noninterest-bearing deposits	(54,937,913)		(65,501,860)
Savings and interest-checking deposits	(88,046,247)		(87,911,463)
Time deposits	(18,968,171)		(10,143,110)
Short-term borrowings	(7,907,884)		(3,554,951)
Long-term borrowings	(7,091,668)		(3,926,489)
Accrued interest payable	(389,251)		(81,356)
Other financial instruments:
Commitments to originate real estate loans for sale	(37,178)		(45,573)
Commitments to sell real estate loans	54,533		54,424
Other credit-related commitments	(155,903)		(148,772)
Interest rate swap agreements used for interest rate risk management	2,133		(7,892)
Interest rate and foreign exchange contracts not designated as hedging instruments	(940,230)		(920,316)
Commercial Loans and Leases [Member] | Significant Unobservable Inputs (Level 3) [Member]
Loans and leases:
Loans and leases	43,817,470		41,139,985
Commercial Loans and Leases [Member] | Carrying Amount [Member]
Loans and leases:
Loans and leases	44,683,549		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	43,817,470		41,139,985
Commercial [Member] | Significant Observable Inputs (Level 2) [Member]
Loans and leases:
Loans and leases	322,029		130,652
Commercial [Member] | Significant Unobservable Inputs (Level 3) [Member]
Loans and leases:
Loans and leases	42,064,780		43,083,994
Commercial [Member] | Carrying Amount [Member]
Loans and leases:
Loans and leases	44,648,711		45,364,571
Commercial [Member] | Cumulative Amount of Fair Value Hedging Adjustment Increasing (Decreasing) the Carrying Amount [Member]
Loans and leases:
Loans and leases	42,386,809		43,214,646
Residential Real Estate Loans | Significant Observable Inputs (Level 2) [Member]
Loans and leases:
Loans and leases	7,256,914		7,049,540
Residential Real Estate Loans | Significant Unobservable Inputs (Level 3) [Member]
Loans and leases:
Loans and leases	14,543,639		14,730,674
Residential Real Estate Loans | Carrying Amount [Member]
Loans and leases:
Loans and leases	23,762,217		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	$ 21,800,553		$ 21,780,214