Summary of Carrying Values, Estimated Fair Values and Fair Value Measurement Levels of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Financial Assets:
Securities held to maturity	$ 5,540,835	[1]	$ 4,705,960	[2]
Mortgage servicing rights	215,055		144,713
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Assets:
Cash and cash equivalents	1,319,710		2,427,258
Financial Liabilities:
Deposits	17,381,704	[3]	15,756,607	[3]
Significant Other Observable Inputs (Level 2)
Financial Assets:
Securities held to maturity	5,535,659		4,648,766
FHLB stock	482,173	[4]	469,145	[4]
Financial Liabilities:
Deposits	7,956,007	[5]	9,152,889	[5]
Borrowed funds	14,151,085		14,935,580
Significant Unobservable Inputs (Level 3)
Financial Assets:
Securities held to maturity	5,177		57,194
Loans, net	31,653,074		31,977,472
Mortgage servicing rights	96		193
Carrying Value
Financial Assets:
Cash and cash equivalents	1,319,710		2,427,258
Securities held to maturity	5,626,605		4,484,262
FHLB stock	482,173	[4]	469,145	[4]
Loans, net	31,638,995		31,580,636
Mortgage servicing rights	96		193
Financial Liabilities:
Deposits	25,287,862		24,877,521
Borrowed funds	12,992,017		13,430,191
Estimated Fair Value
Financial Assets:
Cash and cash equivalents	1,319,710		2,427,258
Securities held to maturity	5,540,835		4,705,960
FHLB stock	482,173	[4]	469,145	[4]
Loans, net	31,653,074		31,977,472
Mortgage servicing rights	96		193
Financial Liabilities:
Deposits	25,337,711		24,909,496
Borrowed funds	$ 14,151,085		$ 14,935,580

[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 June 30, 2013, the non-credit portion of OTTI recorded in AOCL was $9.2 million (before taxes).

[2] At December 31, 2012, the non-credit portion of OTTI recorded in AOCL was $21.6 million (before taxes).

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

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

[5] Certificates of deposit.