Derivatives and Hedging Activities (Derivatives in Statement of Condition) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Derivatives, Fair Value [Line Items]
Derivatives not in hedge accounting relationships: Notional Amount of Derivatives	$ 4,728,160		$ 3,722,415
Derivatives not in hedge accounting relationships: Derivative Assets	17,670		5,682
Derivatives not in hedge accounting relationships: Derivative Liabilities	8,816		7,052
Total derivatives before netting and collateral adjustments: Notional Amount of Derivatives	35,599,805		31,111,550
Total derivatives before netting and collateral adjustments: Derivative Assets	366,947		373,841
Total derivatives before netting and collateral adjustments: Derivative Liabilities	1,146,502		1,313,287
Derivative assets	25,394		36,256
Derivative liabilities as reported on the Statement of Condition	402,355		441,975
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivatives in hedge accounting relationships: Notional Amount of Derivatives	30,871,645		27,389,135
Derivatives in hedge accounting relationships: Derivative Assets	349,277		368,159
Derivatives in hedge accounting relationships: Derivative Liabilities	1,137,686		1,306,235
Derivatives not in hedge accounting relationships: Notional Amount of Derivatives	3,232,597		2,241,681
Derivatives not in hedge accounting relationships: Derivative Assets	15,135		1,378
Derivatives not in hedge accounting relationships: Derivative Liabilities	8,812		7,029
Interest Rate Cap [Member]
Derivatives, Fair Value [Line Items]
Derivatives not in hedge accounting relationships: Notional Amount of Derivatives	1,466,750		1,466,750
Derivatives not in hedge accounting relationships: Derivative Assets	1,858		4,146
Derivatives not in hedge accounting relationships: Derivative Liabilities	0		15
Mortgage Delivery Commitments [Member]
Derivatives, Fair Value [Line Items]
Derivatives not in hedge accounting relationships: Notional Amount of Derivatives	28,813		13,984
Derivatives not in hedge accounting relationships: Derivative Assets	677		158
Derivatives not in hedge accounting relationships: Derivative Liabilities	4		8
Netting Adjustment By Counterparty [Member]
Derivatives, Fair Value [Line Items]
Total collateral and netting adjustments: Derivative Assets	(313,495)		(329,297)
Total collateral and netting adjustments: Derivative Liabilities	(313,495)		(329,297)
Cash Collateral And Related Accrued Interest [Member]
Derivatives, Fair Value [Line Items]
Total collateral and netting adjustments: Derivative Assets	(28,058)		(8,288)
Total collateral and netting adjustments: Derivative Liabilities	(430,652)		542,015
Netting and Collateral [Member]
Derivatives, Fair Value [Line Items]
Total collateral and netting adjustments: Derivative Assets	(341,553)	[1]	(337,585)	[1]
Total collateral and netting adjustments: Derivative Liabilities	$ (744,147)	[1]	$ (871,312)	[1]

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