Loans Troubled Debt Restructurings (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012 contracts	Mar. 31, 2011 contracts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Restructured, Payment Default During Peiriod, Number of Contracts	180	341
Financing Receivable, Restructured, Payment Default During Period, Amortized Cost at Default	$ 19	$ 74