Regulatory Matters (Information On The Capital Ratios) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Capital	$ 2,516,361	$ 2,284,978
Common Equity Tier One Capital Required for Capital Adequacy	$ 979,739	$ 898,972
Common Equity Tier One Capital Ratio	11.56%	11.44%
Common Equity Tier One Capital Required to be Well-Capitalized	$ 1,415,179	$ 1,298,514
Total risk-based capital, Actual Amount	$ 2,950,181	$ 2,722,194
Total risk-based capital, Actual Ratio	13.55%	13.63%
Total risk-based capital, Capital Requirements, Minimum Amount	$ 1,741,758	$ 1,598,172
Total risk-based capital, Capital Requirements, Minimum Ratio	8.00%	8.00%
Total risk-based capital, Capital Requirements, Well Capitalized Amount	$ 2,177,198	$ 1,997,715
Total risk-based capital, Capital Requirements, Well Capitalized Ratio	10.00%	10.00%
Tier 1 risk-based capital, Actual Amount	$ 2,661,398	$ 2,430,015
Tier 1 risk-based capital, Actual Ratio	12.22%	12.16%
Tier 1 risk-based capital, Capital Requirements, Minimum Amount	$ 1,306,319	$ 1,198,629
Tier 1 risk-based capital, Capital Requirements, Minimum Ratio	6.00%	6.00%
Tier 1 risk-based capital, Capital Requirements, Well Capitalized Amount	$ 1,741,758	$ 1,598,172
Tier 1 risk-based capital, Capital Requirements, Well Capitalized Ratio	8.00%	8.00%
Tier 1 leverage capital, Actual Amount	$ 2,661,398	$ 2,430,015
Tier 1 leverage capital, Actual Ratio	8.96%	9.02%
Tier 1 leverage capital, Capital Requirements, Minimum Amount	$ 1,188,507	$ 1,077,303
Tier 1 leverage capital, Capital Requirements, Minimum Ratio	4.00%	4.00%
Tier 1 leverage capital, Capital Requirements, Well Capitalized Amount	$ 1,485,634	$ 1,346,628
Tier 1 leverage capital, Capital Requirements, Well Capitalized Ratio	5.00%	5.00%
Subsidiaries [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Capital	$ 2,527,645	$ 2,170,566
Common Equity Tier One Capital Required for Capital Adequacy	$ 979,497	$ 898,317
Common Equity Tier One Capital Ratio	11.61%	10.87%
Common Equity Tier One Capital Required to be Well-Capitalized	$ 1,414,829	$ 1,297,569
Total risk-based capital, Actual Amount	$ 2,739,108	$ 2,385,425
Total risk-based capital, Actual Ratio	12.58%	11.95%
Total risk-based capital, Capital Requirements, Minimum Amount	$ 1,741,328	$ 1,597,008
Total risk-based capital, Capital Requirements, Minimum Ratio	8.00%	8.00%
Total risk-based capital, Capital Requirements, Well Capitalized Amount	$ 2,176,660	$ 1,996,260
Total risk-based capital, Capital Requirements, Well Capitalized Ratio	10.00%	10.00%
Tier 1 risk-based capital, Actual Amount	$ 2,527,645	$ 2,170,566
Tier 1 risk-based capital, Actual Ratio	11.61%	10.87%
Tier 1 risk-based capital, Capital Requirements, Minimum Amount	$ 1,305,996	$ 1,197,756
Tier 1 risk-based capital, Capital Requirements, Minimum Ratio	6.00%	6.00%
Tier 1 risk-based capital, Capital Requirements, Well Capitalized Amount	$ 1,741,328	$ 1,597,008
Tier 1 risk-based capital, Capital Requirements, Well Capitalized Ratio	8.00%	8.00%
Tier 1 leverage capital, Actual Amount	$ 2,527,645	$ 2,170,566
Tier 1 leverage capital, Actual Ratio	8.51%	8.06%
Tier 1 leverage capital, Capital Requirements, Minimum Amount	$ 1,187,953	$ 1,076,712
Tier 1 leverage capital, Capital Requirements, Minimum Ratio	4.00%	4.00%
Tier 1 leverage capital, Capital Requirements, Well Capitalized Amount	$ 1,484,941	$ 1,345,889
Tier 1 leverage capital, Capital Requirements, Well Capitalized Ratio	5.00%	5.00%
Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Capital Ratio	4.50%	4.50%
Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets [Member] | Subsidiaries [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Capital Ratio	4.50%	4.50%
Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Capital Ratio	6.50%	6.50%
Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets [Member] | Subsidiaries [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Capital Ratio	6.50%	6.50%