Summary of Carrying Values, Estimated Fair Values and Fair Value Measurement Levels of Financial Instruments (Detail) - USD ($) $ in Thousands		Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012
Financial Assets:
Cash and cash equivalents		$ 537,674		$ 564,150		$ 644,550	$ 2,427,258
Securities held to maturity		5,969,390	[1]	6,922,667	[2]
FHLB stock	[3]	663,971		515,327
Loans, net		38,011,995		35,647,639
Financial Liabilities:
Deposits		28,426,758		28,328,734
Borrowed funds		15,748,405		14,226,487
Financial Assets:
Cash and cash equivalents		537,674		564,150
Securities held to maturity		6,108,529	[1]	7,085,971	[2]
FHLB stock	[3]	663,971		515,327
Loans, net		38,245,434		36,167,980
Financial Liabilities:
Deposits		28,408,915		28,377,897
Borrowed funds		15,685,616		15,140,171
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Assets:
Cash and cash equivalents		537,674		564,150
Financial Liabilities:
Deposits	[4]	23,114,271		21,908,136
Significant Other Observable Inputs (Level 2)
Financial Assets:
Securities held to maturity		6,107,697		7,084,959
FHLB stock	[3]	663,971		515,327
Financial Liabilities:
Deposits	[5]	5,294,644		6,469,761
Borrowed funds		15,685,616		15,140,171
Significant Unobservable Inputs (Level 3)
Financial Assets:
Securities held to maturity		832		1,012
Loans, net		$ 38,245,434		$ 36,167,980

[1] Held-to-maturity securities are reported at a carrying amount equal to amortized cost less the non-credit portion of OTTI recorded in AOCL. At December 31, 2015, the non-credit portion of OTTI recorded in AOCL was $8.7 million (before taxes).

[2] Held-to-maturity securities are reported at a carrying amount equal to amortized cost less the non-credit portion of OTTI recorded in AOCL. At December 31, 2014, the non-credit portion of OTTI recorded in AOCL was $8.8 million (before taxes).

[3] Carrying value and estimated fair value are at cost.

[4] NOW and money market accounts, savings accounts, and non-interest-bearing accounts.

[5] Certificates of deposit.