Mortgage Loans Narratives (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Mortgage Loans on Real Estate [Abstract]
Minimum past due months of single-family nonaccrual loans	2 months		2 months		2 months
Carrying value of loans redesignated from HFI to HFS	$ 1,300	$ 19	$ 1,300	$ 33
Average term extension of a single-family modified loan	156 months	133 months	152 months	127 months
Average interest rate reduction of a single-family modified loan	1.66%	2.08%	1.73%	2.23%