Regulatory Capital and Ratios (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2011
Tier 1 Risk-Based Capital
Actual Amount	$ 4,491
Minimum Capital Requirement Amount	782
Minimum to be Well Capitalized Amount	1,173
Actual Ratio	23.00%
Minimum Capital Requirement Ratio	4.00%
Minimum to be Well Capitalized Ratio	6.00%
Total Risk-Based Capital
Actual Amount	4,542
Minimum Capital Requirement Amount	1,563
Minimum to be Well Capitalized Amount	1,954
Actual Ratio	23.20%
Minimum Capital Requirement Ratio	8.00%
Minimum to be Well Capitalized Ratio	10.00%
Tier 1 Core Capital
Actual Amount	4,491
Minimum Capital Requirement Amount	2,356
Minimum to be Well Capitalized Amount	2,945
Actual Ratio	7.60%
Minimum Capital Requirement Ratio	4.00%
Minimum to be Well Capitalized Ratio	5.00%
Tangible Equity
Actual Amount	4,491
Minimum Capital Requirement Amount	$ 1,178
Actual Ratio	7.60%
Minimum Capital Requirement Ratio	2.00%