Fair Value Disclosures (Fair Value Measured on Nonrecurring Basis) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a nonrecurring basis, impaired loans (excluding covered)	$ 67		$ 67		$ 137
Assets measured at fair value on a nonrecurring basis, foreclosed real estate (excluding covered)	89		89		107
Negative valuation adjustments of impaired loans (excluding covered)	14	25	35	55
Negative valuation adjustments of foreclosed real estate (excluding covered)	$ 0	$ 68	$ 2	$ 136