Fair Value of Financial Instruments - Summary of Estimated Fair Values of Financial Instruments not Carried at Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	$ 4,810		$ 5,080
Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	4,810	[1]	5,080	[1]
5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes	348,265		348,209
6.05% Subordinated Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Subordinated Notes	51,528	[2]	51,987	[2]
7.0% Junior Subordinated Debentures
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Junior Subordinated Debentures	54,977		55,020
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	3,862,464		1,538,779
Non-marketable and other securities (cost and equity method accounting)	383,300		378,309
Net commercial loans	9,698,039		9,796,878
Net consumer loans	1,012,327		966,622
FHLB and Federal Reserve Bank stock	40,632		40,632
Accrued interest receivable	70,384		67,772
Non-maturity deposits	25,327,648	[3]	22,259,119	[3]
Time deposits	149,257		213,860
Accrued interest payable	2,866		6,858
Commitments to extend credit	0		0
Carrying Amount | Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	4,810		5,080
Carrying Amount | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes	348,265		348,209
Carrying Amount | 6.05% Subordinated Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Subordinated Notes	51,528	[4]	51,987	[4]
Carrying Amount | 7.0% Junior Subordinated Debentures
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Junior Subordinated Debentures	54,977		55,020
Estimated Fair Value | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	3,862,464		1,538,779
Non-marketable and other securities (cost and equity method accounting)	0		0
Net commercial loans			0
Net consumer loans			0
FHLB and Federal Reserve Bank stock	0		0
Accrued interest receivable	0		0
Non-maturity deposits	25,327,648	[3]	22,259,119	[3]
Time deposits			0
Accrued interest payable	0		0
Commitments to extend credit	0		0
Estimated Fair Value | Level 1 | Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	4,810		5,080
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	[4]	0	[4]
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
Non-marketable and other securities (cost and equity method accounting)	0		0
Net commercial loans			0
Net consumer loans			0
FHLB and Federal Reserve Bank stock	0		0
Accrued interest receivable	70,384		67,772
Non-maturity deposits	0	[3]	0	[3]
Time deposits	149,261		213,874
Accrued interest payable	2,866		6,858
Commitments to extend credit	0		0
Estimated Fair Value | Level 2 | Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	0		0
Estimated Fair Value | Level 2 | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes	388,437		383,782
Estimated Fair Value | Level 2 | 6.05% Subordinated Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Subordinated Notes	55,521	[4]	56,297	[4]
Estimated Fair Value | Level 2 | 7.0% Junior Subordinated Debentures
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Junior Subordinated Debentures	52,289		51,915
Estimated Fair Value | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0		0
Non-marketable and other securities (cost and equity method accounting)	469,899		447,783
Net commercial loans	9,876,872		9,935,917
Net consumer loans	1,068,082		1,005,080
FHLB and Federal Reserve Bank stock	40,632		40,632
Accrued interest receivable	0		0
Non-maturity deposits		[3]	0	[3]
Time deposits			0
Accrued interest payable	0		0
Commitments to extend credit	26,427		24,285
Estimated Fair Value | Level 3 | Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	0		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	[4]	0	[4]
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

[1] Represents cash collateral received from our counterparty for our interest rate swap agreement related to our 6.05% Subordinated Notes.

[2] ncluded in the carrying value of our 6.05% Subordinated Notes at both March 31, 2014 and December 31, 2013 was an interest rate swap valued at $6.0 million related to hedge accounting associated with the notes.

[3] Includes noninterest-bearing demand deposits, interest-bearing checking accounts, money market accounts and interest-bearing sweep deposits.

[4] At March 31, 2014 and December 31, 2013, included in the carrying value and estimated fair value of our 6.05% Subordinated Notes was $6.0 million and $6.5 million, respectively, related to hedge accounting associated with the notes.