Regulatory Capital Ratios for in Comparison With Minimum Amounts and Ratios Required by Federal Reserve Board of Governors (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Common Equity, Tier 1 Amount
Total regulatory capital, Common Equity, Tier 1 Amount	$ 3,869,129	$ 3,748,231
Minimum for capital adequacy purposes, Common Equity, Tier 1 Amount	1,532,448	1,588,699
Excess, Common Equity, Tier 1 Amount	$ 2,336,681	$ 2,159,532
Common Equity, Tier 1 Ratio
Total regulatory capital, Common Equity, Tier 1 Ratio	11.36%	10.62%
Minimum for capital adequacy purposes, Common Equity, Tier 1 Ratio	4.50%	4.50%
Excess, Common Equity, Tier 1 Ratio	6.86%	6.12%
Leverage Capital, Amount
Total regulatory capital, Leverage Capital, Amount	$ 4,371,969	$ 3,748,231
Minimum for capital adequacy purposes, Leverage Capital, Amount	1,826,141	1,875,062
Excess, Leverage Capital, Amount	$ 2,545,828	$ 1,873,169
Leverage Capital, Ratio
Total regulatory capital, Leverage Capital, Ratio	9.58%	8.00%
Minimum for capital adequacy purposes, Leverage Capital, Ratio	4.00%	4.00%
Excess, Leverage Capital, Ratio	5.58%	4.00%
Risk-Based Capital, Tier 1 Amount
Total regulatory capital, Risk-Based Capital, Tier 1 Amount	$ 4,371,969	$ 3,748,231
Minimum for capital adequacy purposes, Risk-Based Capital, Tier 1 Amount	2,043,265	2,118,266
Excess, Risk-Based Capital, Tier 1 Amount	$ 2,328,704	$ 1,629,965
Risk-Based Capital, Tier 1 Ratio
Total regulatory capital, Risk-Based Capital, Tier 1 Ratio	12.84%	10.62%
Minimum for capital adequacy purposes, Risk-Based Capital, Tier 1 Ratio	6.00%	6.00%
Excess, Risk-Based Capital, Tier 1 Ratio	6.84%	4.62%
Risk-Based Capital, Total Amount
Total regulatory capital, Risk-Based Capital, Total Amount	$ 4,877,208	$ 4,277,759
Minimum for capital adequacy purposes, Risk-Based Capital, Total Amount	2,724,353	2,824,355
Excess, Risk-Based Capital, Total Amount	$ 2,152,855	$ 1,453,404
Risk-Based Capital, Total Ratio
Total regulatory capital, Risk-Based Capital, Total Ratio	14.32%	12.12%
Minimum for capital adequacy purposes, Risk-Based Capital, Total Ratio	8.00%	8.00%
Excess, Risk-Based Capital, Total Ratio	6.32%	4.12%