Estimated Fair Values (Fair Value Measured on Recurring Basis) (Details) (USD $)	Sep. 30, 2012		Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets: Mortgage delivery commitments	$ 17,670,000		$ 5,682,000
Derivative assets	25,394,000		36,256,000
Derivative liabilities: Mortgage delivery commitments	8,816,000		7,052,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	4,137,000		4,211,000
AFS securities	1,998,000		1,998,000
Derivative assets: Interest rate related	0		0
Derivative assets	0		0
Total assets at fair value	6,135,000		6,209,000
Derivative liabilities: Interest rate related	0		0
Total derivative liabilities	0		0	[1]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	1,109,878,000		980,074,000
AFS securities	4,842,925,000		2,707,715,000
Derivative assets: Interest rate related	366,270,000		373,683,000
Derivative assets	366,947,000		373,841,000
Total assets at fair value	6,319,750,000		4,061,630,000
Derivative liabilities: Interest rate related	1,146,498,000		1,313,279,000
Total derivative liabilities	1,146,502,000		1,313,287,000	[1]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	0		0
AFS securities	1,481,239,000		1,646,434,000
Derivative assets: Interest rate related	0		0
Derivative assets	0		0
Total assets at fair value	1,481,239,000		1,646,434,000
Derivative liabilities: Interest rate related	0		0
Total derivative liabilities	0		0	[1]
Fair Value, Measurements, Recurring [Member] | Netting and Collateral [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	0	[2]	0	[2]
AFS securities	0	[2]	0	[2]
Derivative assets: Interest rate related	(341,553,000)	[2]	(337,585,000)	[2]
Derivative assets	(341,553,000)	[2]	(337,585,000)	[2]
Total assets at fair value	(341,553,000)	[2]	(337,585,000)	[2]
Derivative liabilities: Interest rate related	(744,147,000)	[2]	(871,312,000)	[2]
Total derivative liabilities	(744,147,000)	[2]	(871,312,000)	[1],[2]
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	1,114,015,000		984,285,000
AFS securities	6,326,162,000		4,356,147,000
Derivative assets: Interest rate related	24,717,000		36,098,000
Derivative assets	25,394,000		36,256,000
Total assets at fair value	7,465,571,000		5,376,688,000
Derivative liabilities: Interest rate related	402,351,000		441,967,000
Total derivative liabilities	402,355,000		441,975,000	[1]
Mortgage Delivery Commitments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets: Mortgage delivery commitments	677,000		158,000
Derivative liabilities: Mortgage delivery commitments	4,000		8,000
Mortgage Delivery Commitments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets: Mortgage delivery commitments	0		0
Derivative liabilities: Mortgage delivery commitments	0		0
Mortgage Delivery Commitments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets: Mortgage delivery commitments	677,000		158,000
Derivative liabilities: Mortgage delivery commitments	4,000		8,000
Mortgage Delivery Commitments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets: Mortgage delivery commitments	0		0
Derivative liabilities: Mortgage delivery commitments	0		0
Mortgage Delivery Commitments [Member] | Fair Value, Measurements, Recurring [Member] | Netting and Collateral [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets: Mortgage delivery commitments	0	[2]	0	[2]
Derivative liabilities: Mortgage delivery commitments	0	[2]	0	[2]
Mortgage Delivery Commitments [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets: Mortgage delivery commitments	677,000		158,000
Derivative liabilities: Mortgage delivery commitments	4,000		8,000
U.S. Treasury Bill Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	0		0
U.S. Treasury Bill Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	1,109,878,000		729,994,000
U.S. Treasury Bill Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	0		0
U.S. Treasury Bill Securities [Member] | Fair Value, Measurements, Recurring [Member] | Netting and Collateral [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	0	[2]	0	[2]
U.S. Treasury Bill Securities [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	1,109,878,000		729,994,000
TLGP Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities			0
TLGP Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities			250,080,000
TLGP Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities			0
TLGP Investments [Member] | Fair Value, Measurements, Recurring [Member] | Netting and Collateral [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities			0	[2]
TLGP Investments [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities			250,080,000
Mutual Funds [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	4,137,000		4,211,000
AFS securities	1,998,000		1,998,000
Mutual Funds [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	0		0
AFS securities	0		0
Mutual Funds [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	0		0
AFS securities	0		0
Mutual Funds [Member] | Fair Value, Measurements, Recurring [Member] | Netting and Collateral [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	0	[2]	0	[2]
AFS securities	0	[2]	0
Mutual Funds [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	4,137,000		4,211,000
AFS securities	1,998,000		1,998,000
Other U.S. obligations [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0
Other U.S. obligations [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	21,020,000
Other U.S. obligations [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0
Other U.S. obligations [Member] | Fair Value, Measurements, Recurring [Member] | Netting and Collateral [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0	[2]
Other U.S. obligations [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	21,020,000
GSE Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0		0
GSE Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	1,374,584,000		900,574,000
GSE Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0		0
GSE Securities [Member] | Fair Value, Measurements, Recurring [Member] | Netting and Collateral [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0	[2]	0	[2]
GSE Securities [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	1,374,584,000		900,574,000
State and local Agency [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0
State and local Agency [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	12,972,000
State and local Agency [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0
State and local Agency [Member] | Fair Value, Measurements, Recurring [Member] | Netting and Collateral [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0	[2]
State and local Agency [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	12,972,000
Other US obligations MBS [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0
Other US obligations MBS [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	326,041,000
Other US obligations MBS [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0
Other US obligations MBS [Member] | Fair Value, Measurements, Recurring [Member] | Netting and Collateral [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0
Other US obligations MBS [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	326,041,000
GSE residential MBS [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0		0
GSE residential MBS [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	3,108,308,000		1,807,141,000
GSE residential MBS [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0		0
GSE residential MBS [Member] | Fair Value, Measurements, Recurring [Member] | Netting and Collateral [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0	[2]	0	[2]
GSE residential MBS [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	3,108,308,000		1,807,141,000
Private label residential MBS [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0		0
Private label residential MBS [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0		0
Private label residential MBS [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	1,466,664,000		1,631,361,000
Private label residential MBS [Member] | Fair Value, Measurements, Recurring [Member] | Netting and Collateral [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0	[2]	0	[2]
Private label residential MBS [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	1,466,664,000		1,631,361,000
HELOCs [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0		0
HELOCs [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0		0
HELOCs [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	14,575,000		15,073,000
HELOCs [Member] | Fair Value, Measurements, Recurring [Member] | Netting and Collateral [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0	[2]	0	[2]
HELOCs [Member] | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	$ 14,575,000		$ 15,073,000

[1] Derivative liabilities represent the total liabilities at fair value.

[2] Amounts represent the effect of legally enforceable master netting agreements on derivatives that allow the Bank to settle positive and negative positions and also cash collateral held or placed with the same counterparties.