Regulatory Matters (Information On The Capital Ratios) (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Capital	$ 2,461,028		$ 2,284,978
Common Equity Tier One Capital Ratio	11.63%		11.44%
Common Equity Tier One Capital Required for Capital Adequacy	$ 952,020		$ 898,972
Common Equity Tier One Capital Required to be Well-Capitalized	1,375,140		1,298,514
Total risk-based capital, Actual Amount	$ 2,895,006		$ 2,722,194
Total risk-based capital, Actual Ratio	13.68%		13.63%
Total risk-based capital, Capital Requirements, Minimum Amount	$ 1,692,480		$ 1,598,172
Total risk-based capital, Capital Requirements, Minimum Ratio	8.00%		8.00%
Total risk-based capital, Capital Requirements, Well Capitalized Amount	$ 2,115,600		$ 1,997,715
Total risk-based capital, Capital Requirements, Well Capitalized Ratio	10.00%		10.00%
Tier 1 capital, Actual Amount	$ 2,606,065		$ 2,430,015
Tier 1 capital, Actual Ratio	12.32%		12.16%
Tier 1 capital, Capital Requirements, Minimum Amount	$ 1,269,360		$ 1,198,629
Tier 1 capital, Capital Requirements, Minimum Ratio	6.00%		6.00%
Tier 1 capital, Capital Requirements, Well Capitalized Amount	$ 1,692,480		$ 1,598,172
Tier 1 capital, Capital Requirements, Well Capitalized Ratio	8.00%		8.00%
Tier 1 leverage capital ratio, Actual Amount	$ 2,606,065		$ 2,430,015
Tier 1 leverage capital ratio, Actual Ratio	8.99%		9.02%
Tier 1 leverage capital ratio, Capital Requirements, Minimum Amount	$ 1,158,906		$ 1,077,303
Tier 1 leverage capital ratio, Capital Requirements, Minimum Ratio	4.00%		4.00%
Tier 1 leverage capital ratio, Capital Requirements, Well Capitalized Amount	$ 1,448,632		$ 1,346,628
Tier 1 leverage capital ratio, Capital Requirements, Well Capitalized Ratio	5.00%		5.00%
Dividends paid	$ 170,000	$ 220,000
Subsidiaries [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Capital	$ 2,617,731		$ 2,170,566
Common Equity Tier One Capital Ratio	12.37%		10.87%
Common Equity Tier One Capital Required for Capital Adequacy	$ 952,532		$ 898,317
Common Equity Tier One Capital Required to be Well-Capitalized	1,375,879		1,297,569
Total risk-based capital, Actual Amount	$ 2,829,352		$ 2,385,425
Total risk-based capital, Actual Ratio	13.37%		11.95%
Total risk-based capital, Capital Requirements, Minimum Amount	$ 1,693,390		$ 1,597,008
Total risk-based capital, Capital Requirements, Minimum Ratio	8.00%		8.00%
Total risk-based capital, Capital Requirements, Well Capitalized Amount	$ 2,116,737		$ 1,996,260
Total risk-based capital, Capital Requirements, Well Capitalized Ratio	10.00%		10.00%
Tier 1 capital, Actual Amount	$ 2,617,731		$ 2,170,566
Tier 1 capital, Actual Ratio	12.37%		10.87%
Tier 1 capital, Capital Requirements, Minimum Amount	$ 1,270,042		$ 1,197,756
Tier 1 capital, Capital Requirements, Minimum Ratio	6.00%		6.00%
Tier 1 capital, Capital Requirements, Well Capitalized Amount	$ 1,693,390		$ 1,597,008
Tier 1 capital, Capital Requirements, Well Capitalized Ratio	8.00%		8.00%
Tier 1 leverage capital ratio, Actual Amount	$ 2,617,731		$ 2,170,566
Tier 1 leverage capital ratio, Actual Ratio	9.04%		8.06%
Tier 1 leverage capital ratio, Capital Requirements, Minimum Amount	$ 1,158,512		$ 1,076,712
Tier 1 leverage capital ratio, Capital Requirements, Minimum Ratio	4.00%		4.00%
Tier 1 leverage capital ratio, Capital Requirements, Well Capitalized Amount	$ 1,448,140		$ 1,345,889
Tier 1 leverage capital ratio, Capital Requirements, Well Capitalized Ratio	5.00%		5.00%
Cash Pass-through Reserve, Federal Home Loan Bank	$ 93,200		$ 81,200
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%