Credit Risk (Details 2) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Jun. 30, 2013 Recourse obligations	Jun. 30, 2013 Capitalized portfolio	Dec. 31, 2012 Capitalized portfolio	Jun. 30, 2012 Capitalized portfolio	Dec. 31, 2011 Capitalized portfolio
Changes in repurchase and foreclosure-related reserves
Balance, beginning of period	$ 191	$ 127
Realized losses	(37)	(66)
Increase in reserves due to:
Changes in assumptions	26	104
New loan sales	11	10
Balance, end of period	191	175
Loans with full risk of loss or with respect to which the company has identified a breach of representation and warranty provisions	196
Percentage of loans with full risk of loss or with respect to which the company has identified a breach of representation and warranty provisions and are at least 90 days delinquent	14.00%
Liabilities for probable losses related to repurchase and indemnification obligations	141		140
Loss contingencies
Estimated amount of reasonably possible losses in excess of the recorded liability				45
Transfers and servicing of loans in servicing portfolio
Servicing portfolio	$ 228,637		$ 183,730		$ 133,061	$ 140,381	$ 147,894	$ 147,088