Actual Capital Amounts and Ratios for Commercial Bank in Comparison With Minimum Amounts and Ratios Required (Detail) - Bank [Member] - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Common Equity, Tier 1 Amount
Total regulatory capital, Common Equity, Tier 1 Amount	$ 4,785,217	$ 4,725,497
Minimum for capital adequacy purposes, Common Equity, Tier 1 Amount	1,733,085	1,623,575
Excess, Common Equity, Tier 1 Amount	$ 3,052,132	$ 3,101,922
Common Equity, Tier 1 Ratio
Total regulatory capital, Common Equity, Tier 1 Ratio	12.42%	13.10%
Minimum for capital adequacy purposes, Common Equity, Tier 1 Ratio	4.50%	4.50%
Excess, Common Equity, Tier 1 Ratio	7.92%	8.60%
Leverage Capital, Amount
Total regulatory capital, Leverage Capital, Amount	$ 4,785,217	$ 4,725,497
Minimum for capital adequacy purposes, Leverage Capital, Amount	1,996,288	1,972,625
Excess, Leverage Capital, Amount	$ 2,788,929	$ 2,752,872
Leverage Capital, Ratio
Total regulatory capital, Leverage Capital, Ratio	9.59%	9.58%
Minimum for capital adequacy purposes, Leverage Capital, Ratio	4.00%	4.00%
Excess, Leverage Capital, Ratio	5.59%	5.58%
Risk-Based Capital, Tier 1 Amount
Total regulatory capital, Risk-Based Capital, Tier 1 Amount	$ 4,785,217	$ 4,725,497
Minimum for capital adequacy purposes, Risk-Based Capital, Tier 1 Amount	2,310,780	2,164,766
Excess, Risk-Based Capital, Tier 1 Amount	$ 2,474,437	$ 2,560,731
Risk-Based Capital, Tier 1 Ratio
Total regulatory capital, Risk-Based Capital, Tier 1 Ratio	12.42%	13.10%
Minimum for capital adequacy purposes, Risk-Based Capital, Tier 1 Ratio	6.00%	6.00%
Excess, Risk-Based Capital, Tier 1 Ratio	6.42%	7.10%
Risk-Based Capital, Total Amount
Total regulatory capital, Risk-Based Capital, Total Amount	$ 4,933,900	$ 4,886,450
Minimum for capital adequacy purposes, Risk-Based Capital, Total Amount	3,081,040	2,886,355
Excess, Risk-Based Capital, Total Amount	$ 1,852,860	$ 2,000,095
Risk-Based Capital, Total Ratio
Total regulatory capital, Risk-Based Capital, Total Ratio	12.81%	13.54%
Minimum for capital adequacy purposes, Risk-Based Capital, Total Ratio	8.00%	8.00%
Excess, Risk-Based Capital, Total Ratio	4.81%	5.54%