Mortgage Loans Narratives (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 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	$ 14	$ 0	$ 14	$ 561
Average term extension of a single-family modified loan	119 months	76 months	124 months	71 months
Average interest rate reduction of a single-family modified loan	2.34%	3.37%	2.30%	3.46%