Fair Value of Financial Instruments - Summary of Estimated Fair Values of Financial Instruments not Carried at Fair Value (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	$ 9,910,504	$ 8,376,138
Loans and Leases Receivable, Net Amount	20,739,970	19,674,578
Short-term FHLB advances
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term FHLB advances	0	500,000
Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other short-term borrowings	470	12,668
3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	347,140	346,979
5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	347,883	347,586
6.05% Subordinated Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Subordinated notes	0	46,646
7.0% Junior Subordinated Debentures
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Junior subordinated debentures	54,406	54,493
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	3,854,244	2,545,750
Held-to-maturity securities	9,938,371	8,426,998
Non-marketable securities (cost and equity method accounting) not measured at net asset value	121,137	120,037
Non-marketable securities (cost and equity method accounting) measured at net asset value	231,029	245,626
FHLB and Federal Reserve Bank stock	58,012	57,592
Accrued interest receivable	119,945	111,222
Non-maturity deposits (1)	42,406,314	38,923,750
Time deposits	58,977	56,118
Accrued interest payable	11,884	12,013
Commitments to extend credit	0	0
Carrying Amount | Short-term FHLB advances
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term FHLB advances		500,000
Carrying Amount | Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other short-term borrowings	470	12,668
Carrying Amount | 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	347,140	346,979
Carrying Amount | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	347,883	347,586
Carrying Amount | 6.05% Subordinated Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Subordinated notes		46,646
Carrying Amount | 7.0% Junior Subordinated Debentures
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Junior subordinated debentures	54,406	54,493
Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	3,854,244	2,545,750
Held-to-maturity securities	9,910,504	8,376,138
Non-marketable securities (cost and equity method accounting) not measured at net asset value	125,649	127,343
Non-marketable securities (cost and equity method accounting) measured at net asset value	344,498	353,870
FHLB and Federal Reserve Bank stock	58,012	57,592
Accrued interest receivable	119,945	111,222
Non-maturity deposits (1)	42,406,314	38,923,750
Time deposits	58,794	55,949
Accrued interest payable	11,884	12,013
Commitments to extend credit	21,848	22,074
Estimated Fair Value | Short-term FHLB advances
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term FHLB advances		500,000
Estimated Fair Value | Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other short-term borrowings	470	12,668
Estimated Fair Value | 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	346,304	337,600
Estimated Fair Value | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	381,609	378,777
Estimated Fair Value | 6.05% Subordinated Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Subordinated notes		47,489
Estimated Fair Value | 7.0% Junior Subordinated Debentures
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Junior subordinated debentures	54,744	53,140
Estimated Fair Value | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	3,854,244	2,545,750
Held-to-maturity securities	0	0
Non-marketable securities (cost and equity method accounting) not measured at net asset value	0	0
FHLB and Federal Reserve Bank stock	0	0
Accrued interest receivable	0	0
Non-maturity deposits (1)	42,406,314	38,923,750
Time deposits	0	0
Accrued interest payable	0	0
Commitments to extend credit	0	0
Estimated Fair Value | Level 1 | Short-term FHLB advances
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term FHLB advances		500,000
Estimated Fair Value | Level 1 | Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other short-term borrowings	470	12,668
Estimated Fair Value | Level 1 | 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	0
Estimated Fair Value | Level 1 | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	0	0
Estimated Fair Value | Level 1 | 6.05% Subordinated Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Subordinated notes		0
Estimated Fair Value | Level 1 | 7.0% Junior Subordinated Debentures
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Junior subordinated debentures	0	0
Estimated Fair Value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Held-to-maturity securities	9,910,504	8,376,138
Non-marketable securities (cost and equity method accounting) not measured at net asset value	0	0
FHLB and Federal Reserve Bank stock	0	0
Accrued interest receivable	119,945	111,222
Non-maturity deposits (1)	0	0
Time deposits	58,794	55,949
Accrued interest payable	11,884	12,013
Commitments to extend credit	0	0
Estimated Fair Value | Level 2 | Short-term FHLB advances
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term FHLB advances		0
Estimated Fair Value | Level 2 | Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other short-term borrowings	0	0
Estimated Fair Value | Level 2 | 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	346,304	337,600
Estimated Fair Value | Level 2 | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	381,609	378,777
Estimated Fair Value | Level 2 | 6.05% Subordinated Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Subordinated notes		47,489
Estimated Fair Value | Level 2 | 7.0% Junior Subordinated Debentures
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Junior subordinated debentures	54,744	53,140
Estimated Fair Value | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Held-to-maturity securities	0	0
Non-marketable securities (cost and equity method accounting) not measured at net asset value	125,649	127,343
FHLB and Federal Reserve Bank stock	58,012	57,592
Accrued interest receivable	0	0
Non-maturity deposits (1)	0	0
Time deposits	0	0
Accrued interest payable	0	0
Commitments to extend credit	21,848	22,074
Estimated Fair Value | Level 3 | Short-term FHLB advances
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term FHLB advances		0
Estimated Fair Value | Level 3 | Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other short-term borrowings	0	0
Estimated Fair Value | Level 3 | 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	0
Estimated Fair Value | Level 3 | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	0	0
Estimated Fair Value | Level 3 | 6.05% Subordinated Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Subordinated notes		0
Estimated Fair Value | Level 3 | 7.0% Junior Subordinated Debentures
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Junior subordinated debentures	0	0
Consumer Portfolio Segment [Member] | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and Leases Receivable, Net Amount	2,389,776	2,156,148
Consumer Portfolio Segment [Member] | Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and Leases Receivable, Net Amount	2,413,582	2,199,501
Consumer Portfolio Segment [Member] | Estimated Fair Value | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and Leases Receivable, Net Amount	0	0
Consumer Portfolio Segment [Member] | Estimated Fair Value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and Leases Receivable, Net Amount	0	0
Consumer Portfolio Segment [Member] | Estimated Fair Value | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and Leases Receivable, Net Amount	2,413,582	2,199,501
Commercial Portfolio Segment | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and Leases Receivable, Net Amount	18,350,194	17,518,430
Commercial Portfolio Segment | Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and Leases Receivable, Net Amount	18,659,199	17,811,356
Commercial Portfolio Segment | Estimated Fair Value | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and Leases Receivable, Net Amount	0	0
Commercial Portfolio Segment | Estimated Fair Value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and Leases Receivable, Net Amount	0	0
Commercial Portfolio Segment | Estimated Fair Value | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and Leases Receivable, Net Amount	18,659,199	$ 17,811,356
Fair Value, Measurements, Recurring | Other derivative instruments | Other liability | Derivatives not designated as hedging instruments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, Liabilities	(11,765)
Fair Value, Measurements, Recurring | Other derivative instruments | Other liability | Derivatives not designated as hedging instruments | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, Liabilities	0
Fair Value, Measurements, Recurring | Other derivative instruments | Other liability | Derivatives not designated as hedging instruments | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, Liabilities	(11,765)
Fair Value, Measurements, Recurring | Other derivative instruments | Other liability | Derivatives not designated as hedging instruments | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, Liabilities	$ 0