Regulatory Matters (Information On The Capital Ratios) (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Mar. 31, 2019	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Capital			$ 2,459,318	$ 2,516,361
Common Equity Tier One Capital Ratio			10.95%	11.56%
Common Equity Tier One Capital Required for Capital Adequacy			$ 1,010,688	$ 979,739
Common Equity Tier One Capital Required to be Well-Capitalized			1,459,883	1,415,179
Total risk-based capital, Actual Amount			$ 2,943,209	$ 2,950,181
Total risk-based capital, Actual Ratio			13.10%	13.55%
Total risk-based capital, Capital Requirements, Minimum Amount			$ 1,796,779	$ 1,741,758
Total risk-based capital, Capital Requirements, Minimum Ratio			8.00%	8.00%
Total risk-based capital, Capital Requirements, Well Capitalized Amount			$ 2,245,974	$ 2,177,198
Total risk-based capital, Capital Requirements, Well Capitalized Ratio			10.00%	10.00%
Tier 1 capital, Actual Amount			$ 2,604,355	$ 2,661,398
Tier 1 capital, Actual Ratio			11.60%	12.22%
Tier 1 capital, Capital Requirements, Minimum Amount			$ 1,347,584	$ 1,306,319
Tier 1 capital, Capital Requirements, Minimum Ratio			6.00%	6.00%
Tier 1 capital, Capital Requirements, Well Capitalized Amount			$ 1,796,779	$ 1,741,758
Tier 1 capital, Capital Requirements, Well Capitalized Ratio			8.00%	8.00%
Tier 1 leverage capital ratio, Actual Amount			$ 2,604,355	$ 2,661,398
Tier 1 leverage capital ratio, Actual Ratio			8.61%	8.96%
Tier 1 leverage capital ratio, Capital Requirements, Minimum Amount			$ 1,209,381	$ 1,188,507
Tier 1 leverage capital ratio, Capital Requirements, Minimum Ratio			4.00%	4.00%
Tier 1 leverage capital ratio, Capital Requirements, Well Capitalized Amount			$ 1,511,727	$ 1,485,634
Tier 1 leverage capital ratio, Capital Requirements, Well Capitalized Ratio			5.00%	5.00%
Dividends paid	$ 80,000	$ 0
Subsidiaries [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Capital			$ 2,596,274	$ 2,527,645
Common Equity Tier One Capital Ratio			11.58%	11.61%
Common Equity Tier One Capital Required for Capital Adequacy			$ 1,009,288	$ 979,497
Common Equity Tier One Capital Required to be Well-Capitalized			1,457,860	1,414,829
Total risk-based capital, Actual Amount			$ 2,857,808	$ 2,739,108
Total risk-based capital, Actual Ratio			12.74%	12.58%
Total risk-based capital, Capital Requirements, Minimum Amount			$ 1,794,289	$ 1,741,328
Total risk-based capital, Capital Requirements, Minimum Ratio			8.00%	8.00%
Total risk-based capital, Capital Requirements, Well Capitalized Amount			$ 2,242,862	$ 2,176,660
Total risk-based capital, Capital Requirements, Well Capitalized Ratio			10.00%	10.00%
Tier 1 capital, Actual Amount			$ 2,596,274	$ 2,527,645
Tier 1 capital, Actual Ratio			11.58%	11.61%
Tier 1 capital, Capital Requirements, Minimum Amount			$ 1,345,717	$ 1,305,996
Tier 1 capital, Capital Requirements, Minimum Ratio			6.00%	6.00%
Tier 1 capital, Capital Requirements, Well Capitalized Amount			$ 1,794,289	$ 1,741,328
Tier 1 capital, Capital Requirements, Well Capitalized Ratio			8.00%	8.00%
Tier 1 leverage capital ratio, Actual Amount			$ 2,596,274	$ 2,527,645
Tier 1 leverage capital ratio, Actual Ratio			8.59%	8.51%
Tier 1 leverage capital ratio, Capital Requirements, Minimum Amount			$ 1,209,218	$ 1,187,953
Tier 1 leverage capital ratio, Capital Requirements, Minimum Ratio			4.00%	4.00%
Tier 1 leverage capital ratio, Capital Requirements, Well Capitalized Amount			$ 1,511,522	$ 1,484,941
Tier 1 leverage capital ratio, 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%