Mortgage Loans Narratives (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Mortgage Loans on Real Estate [Abstract]
Minimum Days Past Due of Single Family Nonaccrual Loans	60 days		60 days		60 days
Carrying value of loans redesignated from HFI to HFS	$ 19	$ 0	$ 33	$ 561
Average term extension of a single-family modified loan	133 months	103 months	127 months	82 months
Average interest rate reduction of a single-family modified loan	2.08%	2.63%	2.23%	3.14%