Fair Value and Investment Securities Narrative Investment Securities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Investment Identifier [Line Items]
Percentage of fair value of investments using discounted cash flow pricing model	10.00%	10.00%
pre-tax impairment available accumulated other compre	$ 3	$ 8
Increase In Impairment Of Securities	$ 2	$ 3
Minimum [Member]
Investment Identifier [Line Items]
ARS, collateralized by student loans with guarantees of principal and interest by the U.S. government via the Department of Education	95.00%
Maximum [Member]
Investment Identifier [Line Items]
ARS, collateralized by student loans with guarantees of principal and interest by the U.S. government via the Department of Education	98.00%