Regulatory Capital and Ratios (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012
Tier 1 Risk-Based Capital
Actual Amount	$ 5,584
Minimum Capital Requirement Amount	1,031
Minimum to be Well Capitalized Amount	1,547
Actual Ratio	21.70%
Minimum Capital Requirement Ratio	4.00%
Minimum to be Well Capitalized Ratio	6.00%
Total Risk-Based Capital
Actual Amount	5,639
Minimum Capital Requirement Amount	2,062
Minimum to be Well Capitalized Amount	2,578
Actual Ratio	21.90%
Minimum Capital Requirement Ratio	8.00%
Minimum to be Well Capitalized Ratio	10.00%
Tier 1 Leverage
Actual Amount	5,584
Minimum Capital Requirement Amount	2,993
Minimum to be Well Capitalized Amount	3,741
Actual Ratio	7.50%
Minimum Capital Requirement Ratio	4.00%
Minimum to be Well Capitalized Ratio	5.00%
Tangible Equity
Actual Amount	5,584
Minimum Capital Requirement Amount	$ 1,496
Actual Ratio	7.50%
Minimum Capital Requirement Ratio	2.00%