Asset Quality (Details 6) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Mar. 31, 2011
Consumer Credit Exposure Credit Risk Profile by Regulatory Classifications
Credit risk profile based on payment	$ 49,226	$ 48,552
Residential, Prime, Financing Receivable [Member]
Consumer Credit Exposure Credit Risk Profile by Regulatory Classifications
Credit risk profile based on payment	11,627	11,851
Pass [Member] | Residential, Prime, Financing Receivable [Member]
Consumer Credit Exposure Credit Risk Profile by Regulatory Classifications
Credit risk profile based on payment	11,399	11,624
Substandard [Member] | Residential, Prime, Financing Receivable [Member]
Consumer Credit Exposure Credit Risk Profile by Regulatory Classifications
Credit risk profile based on payment	$ 228	$ 227