Contingent Liabilities and Guarantees (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012
Guarantees
Maximum Potential Undiscounted Future Payments	$ 13,161
Liability Recorded	177
Standby letters of credit [Member]
Guarantees
Maximum Potential Undiscounted Future Payments	10,137
Liability Recorded	52
Recourse agreement with FNMA [Member]
Guarantees
Maximum Potential Undiscounted Future Payments	973
Liability Recorded	9
Return guarantee agreement with LIHTC investors [Member]
Guarantees
Maximum Potential Undiscounted Future Payments	55
Liability Recorded	55
Return guarantee agreement with LIHTC investors
Compliance period of property	15 years
Expiration of guarantees	Extend through 2018
Written put options [Member]
Guarantees
Maximum Potential Undiscounted Future Payments	1,993
Liability Recorded	60
Default guarantees [Member]
Guarantees
Maximum Potential Undiscounted Future Payments	3
Liability Recorded	$ 1
Risk Level, Low [Member] | Maximum [Member]
Additional Contingent Liabilities and Guarantees (Textual) [Abstract]
Guarantee Obligations	30.00%
Risk Level, Low [Member] | Minimum [Member]
Additional Contingent Liabilities and Guarantees (Textual) [Abstract]
Guarantee Obligations	0.00%
Risk Level, Medium [Member] | Maximum [Member]
Additional Contingent Liabilities and Guarantees (Textual) [Abstract]
Guarantee Obligations	70.00%
Risk Level, Medium [Member] | Minimum [Member]
Additional Contingent Liabilities and Guarantees (Textual) [Abstract]
Guarantee Obligations	31.00%
Risk Level, High [Member] | Maximum [Member]
Additional Contingent Liabilities and Guarantees (Textual) [Abstract]
Guarantee Obligations	100.00%
Risk Level, High [Member] | Minimum [Member]
Additional Contingent Liabilities and Guarantees (Textual) [Abstract]
Guarantee Obligations	71.00%