Regulatory Matters (Information On The Capital Ratios) (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity tier 1, Actual Amount	[1]	$ 1,825,717
Common equity tier 1, Actual Ratio	[1]	10.70%
Common equity tier 1, Capital Requirements, Minimum Amount	[1]	$ 766,928
Common equity tier 1, Capital Requirements, Minimum Ratio	[1]	4.50%
Common equity tier 1, Capital Requirements, Well Capitalized Amount	[1]	$ 1,107,785
Common equity tier 1, Capital Requirements, Well Capitalized Ratio	[1]	6.50%
Total risk-based capital, Actual Amount	[1]	$ 2,201,928	$ 2,096,772
Total risk-based capital, Actual Ratio	[1]	12.90%	14.10%
Total risk-based capital, Capital Requirements, Minimum Amount	[1]	$ 1,363,427	$ 1,192,651
Total risk-based capital, Capital Requirements, Minimum Ratio	[1]	8.00%	8.00%
Total risk-based capital, Capital Requirements, Well Capitalized Amount	[1]	$ 1,704,284	$ 1,490,814
Total risk-based capital, Capital Requirements, Well Capitalized Ratio	[1]	10.00%	10.00%
Tier 1 risk-based capital, Actual Amount	[1]	$ 1,966,829	$ 1,931,276
Tier 1 risk-based capital, Actual Ratio	[1]	11.50%	13.00%
Tier 1 risk-based capital, Capital Requirements, Minimum Amount	[1]	$ 1,022,570	$ 596,326
Tier 1 risk-based capital, Capital Requirements, Minimum Ratio	[1]	6.00%	4.00%
Tier 1 risk-based capital, Capital Requirements, Well Capitalized Amount	[1]	$ 1,363,427	$ 894,488
Tier 1 risk-based capital, Capital Requirements, Well Capitalized Ratio	[1]	8.00%	6.00%
Tier 1 leverage capital, Actual Amount	[1]	$ 1,966,829	$ 1,931,276
Tier 1 leverage capital, Actual Ratio	[1]	8.20%	9.00%
Tier 1 leverage capital, Capital Requirements, Minimum Amount	[1]	$ 954,403	$ 859,241
Tier 1 leverage capital, Capital Requirements, Minimum Ratio	[1]	4.00%	4.00%
Tier 1 leverage capital, Capital Requirements, Well Capitalized Amount	[1]	$ 1,193,004	$ 1,074,051
Tier 1 leverage capital, Capital Requirements, Well Capitalized Ratio	[1]	5.00%	5.00%
Cash Dividends Paid to Parent Company		$ 110,000	$ 100,000
Cash Pass-through Reserve, Federal Home Loan Bank		109,400	38,300
Subsidiaries [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity tier 1, Actual Amount	[1]	$ 1,870,852
Common equity tier 1, Actual Ratio	[1]	11.00%
Common equity tier 1, Capital Requirements, Minimum Amount	[1]	$ 765,232
Common equity tier 1, Capital Requirements, Minimum Ratio	[1]	4.50%
Common equity tier 1, Capital Requirements, Well Capitalized Amount	[1]	$ 1,105,335
Common equity tier 1, Capital Requirements, Well Capitalized Ratio	[1]	6.50%
Total risk-based capital, Actual Amount	[1]	$ 2,047,961	$ 1,939,229
Total risk-based capital, Actual Ratio	[1]	12.00%	13.00%
Total risk-based capital, Capital Requirements, Minimum Amount	[1]	$ 1,360,412	$ 1,190,242
Total risk-based capital, Capital Requirements, Minimum Ratio	[1]	8.00%	8.00%
Total risk-based capital, Capital Requirements, Well Capitalized Amount	[1]	$ 1,700,515	$ 1,487,803
Total risk-based capital, Capital Requirements, Well Capitalized Ratio	[1]	10.00%	10.00%
Tier 1 risk-based capital, Actual Amount	[1]	$ 1,870,852	$ 1,774,814
Tier 1 risk-based capital, Actual Ratio	[1]	11.00%	11.90%
Tier 1 risk-based capital, Capital Requirements, Minimum Amount	[1]	$ 1,020,309	$ 595,121
Tier 1 risk-based capital, Capital Requirements, Minimum Ratio	[1]	6.00%	4.00%
Tier 1 risk-based capital, Capital Requirements, Well Capitalized Amount	[1]	$ 1,360,412	$ 892,682
Tier 1 risk-based capital, Capital Requirements, Well Capitalized Ratio	[1]	8.00%	6.00%
Tier 1 leverage capital, Actual Amount	[1]	$ 1,870,852	$ 1,774,814
Tier 1 leverage capital, Actual Ratio	[1]	7.90%	8.30%
Tier 1 leverage capital, Capital Requirements, Minimum Amount	[1]	$ 953,371	$ 858,197
Tier 1 leverage capital, Capital Requirements, Minimum Ratio	[1]	4.00%	4.00%
Tier 1 leverage capital, Capital Requirements, Well Capitalized Amount	[1]	$ 1,191,714	$ 1,072,746
Tier 1 leverage capital, Capital Requirements, Well Capitalized Ratio	[1]	5.00%	5.00%

[1] Calculated under the Basel III capital standard at December 31, 2015 and under the Basel I capital standard at December 31, 2014.