Summary of Carrying Values, Estimated Fair Values and Fair Value Measurement Levels of Financial Instruments (Detail) - USD ($) $ in Thousands		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 2014
Financial Assets:
Cash and cash equivalents		$ 2,528,169		$ 557,850		$ 537,674	$ 564,150
Securities held to maturity	[1]			3,712,776
FHLB stock	[2]	603,819		590,934
Loans, net		38,265,183		39,308,016
Financial Liabilities:
Deposits		29,102,163		28,887,903
Borrowed funds		12,913,679		13,673,379
Financial Assets:
Cash and cash equivalents		2,528,169
Securities held to maturity	[1]			3,813,959
FHLB stock	[2]	603,819
Loans, net		38,254,538		39,416,469
Financial Liabilities:
Deposits		29,044,852
Borrowed funds		12,780,653
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Assets:
Cash and cash equivalents		2,528,169		557,850
Securities held to maturity				3,813,959
FHLB stock	[2]			590,934
Loans, net				39,416,469
Financial Liabilities:
Deposits		20,458,517	[3]	28,888,064
Borrowed funds				13,633,943
Significant Other Observable Inputs (Level 2)
Financial Assets:
Cash and cash equivalents				557,850
Securities held to maturity				200,220
FHLB stock	[2]	603,819
Financial Liabilities:
Deposits		8,586,335	[4]	21,310,733	[3]
Borrowed funds		12,780,653
Significant Unobservable Inputs (Level 3)
Financial Assets:
Securities held to maturity				3,613,739
FHLB stock	[2]			590,934
Loans, net		$ 38,254,538
Financial Liabilities:
Deposits	[4]			7,577,331
Borrowed funds				$ 13,633,943

[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, 2016, the non-credit portion of OTTI recorded in AOCL was $8.6 million (before taxes).

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

[3] Interest-bearing checking and money market accounts, savings accounts, and non-interest-bearing accounts.

[4] Certificates of deposit.