Mortgage Loans Held for Portfolio (Details 2) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Participating Mortgage Loans [Line Items]
Unpaid Principal Balances Greater Than Five Percent of Total	$ 3,798		$ 4,233
Percent of Total	53.00%		58.00%
Union Savings Bank [Member]
Participating Mortgage Loans [Line Items]
Unpaid Principal Balances Greater Than Five Percent of Total	1,724		1,984
Percent of Total	24.00%		27.00%
PNC Bank, N.A. [Member]
Participating Mortgage Loans [Line Items]
Unpaid Principal Balances Greater Than Five Percent of Total	1,695	[1]	1,818	[1]
Percent of Total	24.00%	[1]	25.00%	[1]
Guardian Saving Bank FSB [Member]
Participating Mortgage Loans [Line Items]
Unpaid Principal Balances Greater Than Five Percent of Total	$ 379		$ 431
Percent of Total	5.00%		6.00%

[1] Former member.