Fair Value of Financial Instruments - Summary of Estimated Fair Values of Financial Instruments not Carried at Fair Value (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Derivative Liabilities	$ (97,204)	$ (108,581)
Held-to-maturity securities	15,493,995	12,548,280
Loans and Leases Receivable, Net Amount	25,709,483	22,851,292
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	2,712,101	2,923,075
Held-to-maturity securities	15,898,263	12,663,455
Non-marketable securities not measured at net asset value	116,484	120,019
Non-marketable securities measured at net asset value	136,010	228,399
FHLB and Federal Reserve Bank stock	58,864	60,020
Non-maturity deposits	48,825,291	44,206,929
Time deposits	62,004	47,146
Commitments to extend credit	0	0
Carrying Amount | Short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	417,246	1,033,730
Carrying Amount | 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	347,470	347,303
Carrying Amount | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	348,502	348,189
Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	2,712,101	2,923,075
Held-to-maturity securities	15,493,995	12,548,280
Non-marketable securities not measured at net asset value	116,484	126,345
Non-marketable securities measured at net asset value	136,010	331,496
FHLB and Federal Reserve Bank stock	58,864	60,020
Non-maturity deposits	48,825,291	44,206,929
Time deposits	61,732	46,885
Commitments to extend credit	23,553	22,208
Estimated Fair Value | Short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	417,246	1,033,730
Estimated Fair Value | 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	339,283	352,058
Estimated Fair Value | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	364,980	374,483
Estimated Fair Value | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	2,712,101	2,923,075
Held-to-maturity securities	0	0
Non-marketable securities not measured at net asset value	0	0
FHLB and Federal Reserve Bank stock	0	0
Non-maturity deposits	48,825,291	44,206,929
Time deposits	0	0
Commitments to extend credit	0	0
Estimated Fair Value | Level 1 | Short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	417,246	1,033,730
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 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Held-to-maturity securities	15,493,995	12,548,280
Non-marketable securities not measured at net asset value	0	0
FHLB and Federal Reserve Bank stock	0	0
Non-maturity deposits	0	0
Time deposits	61,732	46,885
Commitments to extend credit	0	0
Estimated Fair Value | Level 2 | Short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
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	339,283	352,058
Estimated Fair Value | Level 2 | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	364,980	374,483
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 not measured at net asset value	116,484	126,345
FHLB and Federal Reserve Bank stock	58,864	60,020
Non-maturity deposits	0	0
Time deposits	0	0
Commitments to extend credit	23,553	22,208
Estimated Fair Value | Level 3 | Short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
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
Consumer loans | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and Leases Receivable, Net Amount	2,859,782	2,613,045
Consumer loans | Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and Leases Receivable, Net Amount	2,872,681	2,593,538
Consumer loans | Estimated Fair Value | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and Leases Receivable, Net Amount	0	0
Consumer loans | Estimated Fair Value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and Leases Receivable, Net Amount	0	0
Consumer loans | Estimated Fair Value | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and Leases Receivable, Net Amount	2,872,681	2,593,538
Commercial loans | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and Leases Receivable, Net Amount	22,849,701	20,238,247
Commercial loans | Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and Leases Receivable, Net Amount	23,139,492	20,520,623
Commercial loans | Estimated Fair Value | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and Leases Receivable, Net Amount	0	0
Commercial loans | Estimated Fair Value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and Leases Receivable, Net Amount	0	0
Commercial loans | Estimated Fair Value | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and Leases Receivable, Net Amount	23,139,492	$ 20,520,623
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, Derivative Liabilities	(12,532)
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, Derivative 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, Derivative Liabilities	(12,532)
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, Derivative Liabilities	$ 0