Fair Value (Fair Value Option Election) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value Option Election, Unpaid Principal Balance [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Mortgages Held-for-sale, Fair Value Disclosure	$ 731	$ 2,416
Fair Value Option Election, Unpaid Principal Balance [Member] | Mortgage Loans Held For Sale, Net [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value, Option, Loans Held as Assets, Aggregate Amount in Nonaccrual Status	50	47
Fair Value, Option, Loans Held as Assets, 90 Days or More Past Due	41	36
Fair Value Option Election, Fair Value [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Mortgages Held-for-sale, Fair Value Disclosure	701	2,490
Fair Value Option Election, Fair Value [Member] | Mortgage Loans Held For Sale, Net [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value, Option, Loans Held as Assets, Aggregate Amount in Nonaccrual Status	26	25
Fair Value, Option, Loans Held as Assets, 90 Days or More Past Due	$ 21	$ 19