Fair Value Measurements (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2011	Mar. 31, 2012	Dec. 31, 2011
Fair Value, Liabilities Measured on Recurring Basis Unobservable Input Reconciliation
Impaired loans		$ 589	$ 575
Level 2 | Financial Products
Fair Value, Liabilities Measured on Recurring Basis Unobservable Input Reconciliation
Impaired loans		133	141
Level 3 | Guarantees
Fair Value, Liabilities Measured on Recurring Basis Unobservable Input Reconciliation
Balance	10	7	7
Issuance of guarantees	1
Expiration of guarantees	(1)
Balance	$ 10	$ 7	$ 7