Regulatory Capital Amounts and Ratios in Comparison with Minimum Requirement by FRB for Capital Adequacy Purposes (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Leverage Capital Amount
Total regulatory capital, Leverage Capital Amount	$ 3,580,302	$ 3,503,672
Minimum for capital adequacy purposes, Leverage Capital Amount	1,575,464	1,544,875
Excess, Leverage Capital Amount	2,004,838	1,958,797
Leverage Capital Ratio
Total regulatory capital, Leverage Capital Ratio	9.09%	9.07%
Minimum for capital adequacy purposes, Leverage Capital Ratio	4.00%	4.00%
Excess, Leverage Capital Ratio	5.09%	5.07%
Tier 1 Amount
Total regulatory capital, Risk-Based Capital, Tier 1 Amount	3,580,302	3,503,672
Minimum for capital adequacy purposes, Risk-Based Capital, Tier 1 Amount	1,054,144	1,023,848
Excess, Risk-Based Capital, Tier 1 Amount	2,526,158	2,479,824
Tier 1 Ratio
Total regulatory capital, Risk-Based Capital, Tier 1 Ratio	13.59%	13.69%
Minimum for capital adequacy purposes, Risk-Based Capital, Tier 1 Ratio	4.00%	4.00%
Excess, Risk-Based Capital, Tier 1 Ratio	9.59%	9.69%
Total Amount
Total regulatory capital, Risk-Based Capital, Total Amount	3,750,915	3,674,679
Minimum for capital adequacy purposes, Risk-Based Capital, Total Amount	2,108,287	2,047,696
Excess, Risk-Based Capital, Total Amount	$ 1,642,628	$ 1,626,983
Total Ratio
Total regulatory capital, Risk-Based Capital, Total Ratio	14.23%	14.36%
Minimum for capital adequacy purposes, Risk-Based Capital, Total Ratio	8.00%	8.00%
Excess, Risk-Based Capital, Total Ratio	6.23%	6.36%