Regulatory Matters (Information On The Capital Ratios) (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Capital	$ 2,000,421		$ 1,932,171
Common Equity Tier One Capital Ratio	10.84%		10.52%
Common Equity Tier One Capital Required for Capital Adequacy	$ 830,190		$ 826,504
Common Equity Tier One Capital Required to be Well-Capitalized	1,199,163		1,193,840
Total risk-based capital, Actual Amount	$ 2,402,573		$ 2,328,808
Total risk-based capital, Actual Ratio	13.02%		12.68%
Total risk-based capital, Capital Requirements, Minimum Amount	$ 1,475,893		$ 1,469,341
Total risk-based capital, Capital Requirements, Minimum Ratio	8.00%		8.00%
Total risk-based capital, Capital Requirements, Well Capitalized Amount	$ 1,844,867		$ 1,836,677
Total risk-based capital, Capital Requirements, Well Capitalized Ratio	10.00%		10.00%
Tier 1 capital, Actual Amount	$ 2,123,131		$ 2,054,881
Tier 1 capital, Actual Ratio	11.51%		11.19%
Tier 1 capital, Capital Requirements, Minimum Amount	$ 1,106,920		$ 1,102,006
Tier 1 capital, Capital Requirements, Minimum Ratio	6.00%		6.00%
Tier 1 capital, Capital Requirements, Well Capitalized Amount	$ 1,475,893		$ 1,469,341
Tier 1 capital, Capital Requirements, Well Capitalized Ratio	8.00%		8.00%
Tier 1 leverage capital ratio, Actual Amount	$ 2,123,131		$ 2,054,881
Tier 1 leverage capital ratio, Actual Ratio	8.28%		8.13%
Tier 1 leverage capital ratio, Capital Requirements, Minimum Amount	$ 1,025,965		$ 1,010,857
Tier 1 leverage capital ratio, Capital Requirements, Minimum Ratio	4.00%		4.00%
Tier 1 leverage capital ratio, Capital Requirements, Well Capitalized Amount	$ 1,282,457		$ 1,263,571
Tier 1 leverage capital ratio, Capital Requirements, Well Capitalized Ratio	5.00%		5.00%
Dividends paid	$ 30,000	$ 85,000
Subsidiaries [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Capital	$ 2,042,747		$ 1,945,332
Common Equity Tier One Capital Ratio	11.08%		10.61%
Common Equity Tier One Capital Required for Capital Adequacy	$ 829,365		$ 825,228
Common Equity Tier One Capital Required to be Well-Capitalized	1,197,972		1,191,995
Total risk-based capital, Actual Amount	$ 2,244,869		$ 2,141,939
Total risk-based capital, Actual Ratio	12.18%		11.68%
Total risk-based capital, Capital Requirements, Minimum Amount	$ 1,474,427		$ 1,467,071
Total risk-based capital, Capital Requirements, Minimum Ratio	8.00%		8.00%
Total risk-based capital, Capital Requirements, Well Capitalized Amount	$ 1,843,034		$ 1,833,839
Total risk-based capital, Capital Requirements, Well Capitalized Ratio	10.00%		10.00%
Tier 1 capital, Actual Amount	$ 2,042,747		$ 1,945,332
Tier 1 capital, Actual Ratio	11.08%		10.61%
Tier 1 capital, Capital Requirements, Minimum Amount	$ 1,105,821		$ 1,100,304
Tier 1 capital, Capital Requirements, Minimum Ratio	6.00%		6.00%
Tier 1 capital, Capital Requirements, Well Capitalized Amount	$ 1,474,427		$ 1,467,071
Tier 1 capital, Capital Requirements, Well Capitalized Ratio	8.00%		8.00%
Tier 1 leverage capital ratio, Actual Amount	$ 2,042,747		$ 1,945,332
Tier 1 leverage capital ratio, Actual Ratio	7.97%		7.70%
Tier 1 leverage capital ratio, Capital Requirements, Minimum Amount	$ 1,025,265		$ 1,010,005
Tier 1 leverage capital ratio, Capital Requirements, Minimum Ratio	4.00%		4.00%
Tier 1 leverage capital ratio, Capital Requirements, Well Capitalized Amount	$ 1,281,581		$ 1,262,507
Tier 1 leverage capital ratio, Capital Requirements, Well Capitalized Ratio	5.00%		5.00%
Cash Pass-through Reserve, Federal Home Loan Bank	$ 71,000		$ 58,600
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%