Condensed Statements of Condition (Detail) - USD ($) $ in Thousands	Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
ASSETS:
Cash and cash equivalents	$ 2,528,169		$ 557,850	$ 537,674	$ 564,150
Securities available for sale	3,531,427	[1]	104,281
Other assets	401,138		387,413
Total assets	49,124,195		48,926,555	50,317,796
LIABILITIES AND STOCKHOLDERS' EQUITY:
Junior subordinated debentures	359,179		358,879
Other liabilities	312,977		241,282
Total liabilities	42,328,819		42,802,564
Stockholders' equity	6,795,376		6,123,991	5,934,696
Total liabilities and stockholders' equity	49,124,195		48,926,555
Parent Company
ASSETS:
Cash and cash equivalents	90,536		63,727	$ 70,380	$ 89,518
Securities available for sale			2,002
Investments in subsidiaries	7,050,139		6,426,276
Receivables from subsidiaries	4,750		7,839
Other assets	23,980		34,102
Total assets	7,169,405		6,533,946
LIABILITIES AND STOCKHOLDERS' EQUITY:
Junior subordinated debentures	359,179		358,879
Other liabilities	14,850		51,076
Total liabilities	374,029		409,955
Stockholders' equity	6,795,376		6,123,991
Total liabilities and stockholders' equity	$ 7,169,405		$ 6,533,946

[1] The amortized cost includes the non-credit portion of OTTI recorded in AOCL. At December 31, 2017, the non-credit portion of OTTI recorded in AOCL was $8.6 million (before taxes).