Advances (Year of Contractual Maturity or Next Call Date) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Advances [Abstract]
Overdrawn Demand Deposit Accounts	$ 459	$ 0
Federal Home Loan Bank Advances, Earlier of Contractual Maturity or Next Call Date, Due With in Next Rolling Twelve Months	15,273,108
Federal Home Loan Bank, Advances, Earlier of Contractual Maturity or Next Call Date, Due within One Year of Balance Sheet Date		20,726,461
Federal Home Loan Bank Advances Earlier of Contractual Maturity or Next Call Date Due in Rolling Year Two	6,537,812
Federal Home Loan Bank, Advances, Earlier of Contractual Maturity or Next Call Date, Due From One To Two Years of Balance Sheet Date		3,563,705
Federal Home Loan Bank Advances Earlier of Contractual Maturity or Next Call Date Due in Rolling Year Three	5,330,611
Federal Home Loan Bank, Advances, Earlier of Contractual Maturity or Next Call Date, Due From Two To Three Years of Balance Sheet Date		4,776,457
Federal Home Loan Bank Advances Earlier of Contractual Maturity or Next Call Date Due in Rolling Year Four	6,259,501
Federal Home Loan Bank, Advances, Earlier of Contractual Maturity or Next Call Date, Due From Three To Four Years of Balance Sheet Date		3,746,205
Federal Home Loan Bank Advances Earlier of Contractual Maturity or Next Call Date Due in Rolling Year Five	7,110,019
Federal Home Loan Bank, Advances, Earlier of Contractual Maturity or Next Call Date, Due From Four To Five Years of Balance Sheet Date		6,732,368
Federal Home Loan Bank Advances Earlier of Contractual Maturity or Next Call Date Due After Rolling Year Five	17,487,542
Federal Home Loan Bank, Advances, Earlier of Contractual Maturity or Next Call Date, Due After Five Years of Balance Sheet Date		14,075,582
Federal Home Loan Bank Advances At Par Value	$ 57,999,052	$ 53,620,778