Variable Interest Entities - Carrying Amounts and Classification of Significant Variable Interests (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Cash and cash equivalents	$ 2,712,101	$ 2,923,075	$ 3,854,244	$ 2,545,750
Non-marketable and other equity securities	852,505	651,053
Accrued interest receivable and other assets	984,424	876,246
Total assets	55,867,745	51,214,467
Other liabilities	1,062,391	911,755
Total liabilities	51,062,904	46,895,052
Maximum exposure to loss in unconsolidated VIEs	529,429	346,097
Investments in qualified affordable housing projects, net	251,479	174,214
Other liabilities consisting of unfunded commitments	161,113	100,891
Consolidated
Variable Interest Entity [Line Items]
Cash and cash equivalents	4,113	6,674
Non-marketable and other equity securities	208,275	190,562
Accrued interest receivable and other assets	397	365
Total assets	212,785	197,601
Other liabilities	765	990
Total liabilities	765	990
Maximum exposure to loss in unconsolidated VIEs	212,000
Unconsolidated
Variable Interest Entity [Line Items]
Cash and cash equivalents	0	0
Non-marketable and other equity securities	529,429	346,097
Accrued interest receivable and other assets	0	0
Total assets	529,429	346,097
Other liabilities	161,113	100,891
Total liabilities	$ 161,113	$ 100,891