Variable Interest Entities - Carrying Amounts and Classification of Significant Variable Interests (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Cash and cash equivalents	$ 3,819,141	$ 2,923,075	$ 3,555,571	$ 2,545,750
Non-marketable and other equity securities	896,249	651,053
Accrued interest receivable and other assets	1,105,917	876,246
Total assets	58,139,734	51,214,467
Other liabilities	1,146,109	911,755
Total liabilities	53,069,689	46,895,052
Maximum exposure to loss in unconsolidated VIEs	524,812	346,097
Investments in qualified affordable housing projects, net	261,706	174,214
Other liabilities consisting of unfunded commitments related to qualified affordable housing projects	166,867	100,891
Consolidated
Variable Interest Entity [Line Items]
Cash and cash equivalents	5,470	6,674
Non-marketable and other equity securities	212,514	190,562
Accrued interest receivable and other assets	298	365
Total assets	218,282	197,601
Other liabilities	680	990
Total liabilities	680	990
Maximum exposure to loss in unconsolidated VIEs	217,600
Unconsolidated
Variable Interest Entity [Line Items]
Cash and cash equivalents	0	0
Non-marketable and other equity securities	524,812	346,097
Accrued interest receivable and other assets	0	0
Total assets	524,812	346,097
Other liabilities	166,867	100,891
Total liabilities	$ 166,867	$ 100,891