Fair Value of Financial Instruments Summary of Estimated Fair Values of Financial Instruments not Carried at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity Securities, Fair Value	$ 8,758,622	$ 7,415,656
Federal Home Loan Bank Advances	638,000	0
Short-term borrowings	774,900	7,781
Time Deposits	70,479	128,127
Federal Funds Purchased
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	135,000	0
Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	1,900	7,781
3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes	346,667	0
5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes	347,016	346,477
6.05% Subordinated Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Subordinated Notes	48,350	50,040
7.0% Junior Subordinated Debentures
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Junior Subordinated Debentures	54,669	54,845
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	1,503,257	1,796,062
Held-to-maturity Securities, Fair Value	8,790,963	7,421,042
Non-marketable securities (cost and equity method accounting)	114,795	108,221
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Non-Marketable Securities	250,970	188,427
Net commercial loans	14,763,302	12,947,869
Net consumer loans	1,761,155	1,271,048
FHLB and FRB stock	56,991	53,496
Accrued interest receivable	107,604	94,180
Deposits	39,072,297	34,215,372
Time Deposits	70,479	128,127
Accrued interest payable	12,058	6,998
Commitments to extend credit	0	0
Carrying Amount | Federal Funds Purchased
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	135,000
Carrying Amount | Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	1,900	7,781
Carrying Amount | 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes	346,667
Carrying Amount | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes	347,016	346,477
Carrying Amount | 6.05% Subordinated Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Subordinated Notes	48,350	50,040
Carrying Amount | 7.0% Junior Subordinated Debentures
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Junior Subordinated Debentures	54,669	54,845
Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	1,503,257	1,796,062
Held-to-maturity Securities, Fair Value	8,758,622	7,415,656
Non-marketable securities (cost and equity method accounting)	117,172	107,451
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Non-Marketable Securities	364,799	283,119
Net commercial loans	14,811,588	13,082,487
Net consumer loans	1,737,960	1,247,336
FHLB and FRB stock	56,991	53,496
Accrued interest receivable	107,604	94,180
Federal Home Loan Bank Advances	638,000
Deposits	39,072,297	34,215,372
Time Deposits	70,347	128,107
Accrued interest payable	12,058	6,998
Commitments to extend credit	26,483	29,097
Assets Held-for-sale, Long Lived, Fair Value Disclosure		45,400
Estimated Fair Value | Federal Funds Purchased
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	135,000
Estimated Fair Value | Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	1,900	7,781
Estimated Fair Value | 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes	333,648
Estimated Fair Value | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes	384,216	392,616
Estimated Fair Value | 6.05% Subordinated Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Subordinated Notes	49,820	53,537
Estimated Fair Value | 7.0% Junior Subordinated Debentures
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Junior Subordinated Debentures	52,905	52,990
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	1,503,257	1,796,062
Held-to-maturity Securities, Fair Value	0	0
Non-marketable securities (cost and equity method accounting)	0	0
Net commercial loans	0	0
Net consumer loans	0	0
FHLB and FRB stock	0	0
Accrued interest receivable	0	0
Federal Home Loan Bank Advances	638,000
Deposits	39,072,297	34,215,372
Time Deposits	0	0
Accrued interest payable	0	0
Commitments to extend credit	0	0
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1) | Federal Funds Purchased
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	135,000
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	1,900	7,781
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1) | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes	0	0
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1) | 6.05% Subordinated Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Subordinated Notes	0	0
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (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 | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Held-to-maturity Securities, Fair Value	8,758,622	7,415,656
Non-marketable securities (cost and equity method accounting)	0	0
Net commercial loans	0	0
Net consumer loans	0	0
FHLB and FRB stock	0	0
Accrued interest receivable	107,604	94,180
Deposits	0	0
Time Deposits	70,347	128,107
Accrued interest payable	12,058	6,998
Commitments to extend credit	0	0
Estimated Fair Value | Significant Other Observable Inputs (Level 2) | Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	0	0
Estimated Fair Value | Significant Other Observable Inputs (Level 2) | 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes	333,648
Estimated Fair Value | Significant Other Observable Inputs (Level 2) | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes	384,216	392,616
Estimated Fair Value | Significant Other Observable Inputs (Level 2) | 6.05% Subordinated Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Subordinated Notes	49,820	53,537
Estimated Fair Value | Significant Other Observable Inputs (Level 2) | 7.0% Junior Subordinated Debentures
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Junior Subordinated Debentures	52,905	52,990
Estimated Fair Value | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Held-to-maturity Securities, Fair Value	0	0
Non-marketable securities (cost and equity method accounting)	117,172	107,451
Net commercial loans	14,811,588	13,082,487
Net consumer loans	1,737,960	1,247,336
FHLB and FRB stock	56,991	53,496
Accrued interest receivable	0	0
Deposits	0	0
Time Deposits	0	0
Accrued interest payable	0	0
Commitments to extend credit	26,483	29,097
Estimated Fair Value | Significant Unobservable Inputs (Level 3) | Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	0	0
Estimated Fair Value | Significant Unobservable Inputs (Level 3) | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes	0	0
Estimated Fair Value | Significant Unobservable Inputs (Level 3) | 6.05% Subordinated Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Subordinated Notes	0	0
Estimated Fair Value | Significant Unobservable Inputs (Level 3) | 7.0% Junior Subordinated Debentures
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Junior Subordinated Debentures	$ 0	0
Global Commercial Bank | SVB India Finance Private Limited, (SVBIF)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Disposal Group, Including Discontinued Operation, Assets		$ 44,300