Actual Capital Amounts and Ratios for Commercial Bank in Comparison With Minimum Amounts and Ratios Required (Detail) - Bank [Member] - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Common Equity, Tier 1 Amount
Total regulatory capital, Common Equity, Tier 1 Amount	$ 4,725,497	$ 4,253,233
Minimum for capital adequacy purposes, Common Equity, Tier 1 Amount	1,623,575	1,424,795
Excess, Common Equity, Tier 1 Amount	$ 3,101,922	$ 2,828,438
Common Equity, Tier 1 Ratio
Total regulatory capital, Common Equity, Tier 1 Ratio	13.10%	13.43%
Minimum for capital adequacy purposes, Common Equity, Tier 1 Ratio	4.50%	4.50%
Excess, Common Equity, Tier 1 Ratio	8.60%	8.93%
Leverage Capital, Amount
Total regulatory capital, Leverage Capital, Amount	$ 4,725,497	$ 4,253,233
Minimum for capital adequacy purposes, Leverage Capital, Amount	1,972,625	1,691,041
Excess, Leverage Capital, Amount	$ 2,752,872	$ 2,562,192
Leverage Capital, Ratio
Total regulatory capital, Leverage Capital, Ratio	9.58%	10.06%
Minimum for capital adequacy purposes, Leverage Capital, Ratio	4.00%	4.00%
Excess, Leverage Capital, Ratio	5.58%	6.06%
Risk-Based Capital, Tier 1 Amount
Total regulatory capital, Risk-Based Capital, Tier 1 Amount	$ 4,725,497	$ 4,253,233
Minimum for capital adequacy purposes, Risk-Based Capital, Tier 1 Amount	2,164,766	1,899,727
Excess, Risk-Based Capital, Tier 1 Amount	$ 2,560,731	$ 2,353,506
Risk-Based Capital, Tier 1 Ratio
Total regulatory capital, Risk-Based Capital, Tier 1 Ratio	13.10%	13.43%
Minimum for capital adequacy purposes, Risk-Based Capital, Tier 1 Ratio	6.00%	6.00%
Excess, Risk-Based Capital, Tier 1 Ratio	7.10%	7.43%
Risk-Based Capital, Total Amount
Total regulatory capital, Risk-Based Capital, Total Amount	$ 4,886,450	$ 4,387,620
Minimum for capital adequacy purposes, Risk-Based Capital, Total Amount	2,886,355	2,532,969
Excess, Risk-Based Capital, Total Amount	$ 2,000,095	$ 1,854,651
Risk-Based Capital, Total Ratio
Total regulatory capital, Risk-Based Capital, Total Ratio	13.54%	13.86%
Minimum for capital adequacy purposes, Risk-Based Capital, Total Ratio	8.00%	8.00%
Excess, Risk-Based Capital, Total Ratio	5.54%	5.86%