Derivatives and Hedging Activities (Derivatives in Statement of Condition) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Derivative Instruments in Hedges, Assets, at Fair Value	$ 62,134		$ 95,611
Derivative Instruments in Hedges, Liabilities, at Fair Value	963,100		1,335,915
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	20,124		23,103
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	6,800		8,673
Derivative Asset, Fair Value, Gross Asset	82,258		118,714
Derivative Liability, Fair Value, Gross Liability	969,900		1,344,588
Derivative Asset, Fair Value, Amount Offset Against Collateral	(67,817)	[1]	(104,767)	[1]
Derivative Liability, Fair Value, Amount Offset Against Collateral	(959,904)	[1]	(1,333,320)	[1]
Derivative Assets	14,441		13,947
Derivative liabilities	9,996		11,268
Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	33,971,718		40,597,022
Interest Rate Swaptions Related to Optional Advance Commitments [Member]
Derivatives, Fair Value [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	0		0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	0		0
Cash Collateral And Related Accrued Interest [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Offset Against Collateral	(937)		0
Derivative Liability, Fair Value, Amount Offset Against Collateral	(893,024)		(1,228,553)
Netting Adjustment By Counterparty [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Offset Against Collateral	(66,880)		(104,767)
Derivative Liability, Fair Value, Amount Offset Against Collateral	(66,880)		(104,767)
Advances [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative Instruments in Hedges, Assets, at Fair Value	13,081		115
Derivative Instruments in Hedges, Liabilities, at Fair Value	273,413		521,397
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	0		0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	45		59
Advances [Member] | Interest Rate Cap [Member]
Derivatives, Fair Value [Line Items]
Derivative Instruments in Hedges, Assets, at Fair Value	6		9
Derivative Instruments in Hedges, Liabilities, at Fair Value	0		0
Available-for-sale Securities [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative Instruments in Hedges, Assets, at Fair Value	7,013		30
Derivative Instruments in Hedges, Liabilities, at Fair Value	584,956		797,572
Unsecured Debt [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative Instruments in Hedges, Assets, at Fair Value	42,034		95,457
Derivative Instruments in Hedges, Liabilities, at Fair Value	104,731		16,946
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	0		969
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	0		0
Basis Swap [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	12,181		13,001
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	0		0
Intermediary Transactions [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	4,167		7,029
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	3,939		6,805
Intermediary Transactions [Member] | Interest Rate Cap [Member]
Derivatives, Fair Value [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	2,816		1,809
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	2,816		1,809
Held-to-maturity Securities [Member] | Interest Rate Cap [Member]
Derivatives, Fair Value [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	960		295
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	0		0
Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	8,035,696		9,519,446
Not Designated as Hedging Instrument [Member] | Interest Rate Swaptions Related to Optional Advance Commitments [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	0		50,000
Not Designated as Hedging Instrument [Member] | Advances [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	14,800		5,292
Not Designated as Hedging Instrument [Member] | Unsecured Debt [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	0		650,000
Not Designated as Hedging Instrument [Member] | Basis Swap [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	3,700,000		4,700,000
Not Designated as Hedging Instrument [Member] | Intermediary Transactions [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	110,896		104,154
Not Designated as Hedging Instrument [Member] | Intermediary Transactions [Member] | Interest Rate Cap [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	110,000		110,000
Not Designated as Hedging Instrument [Member] | Held-to-maturity Securities [Member] | Interest Rate Cap [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	4,100,000		3,900,000
Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	25,936,022		31,077,576
Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Advances [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	5,041,678		6,723,412
Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Advances [Member] | Interest Rate Cap [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	25,000		28,000
Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Available-for-sale Securities [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	4,924,934		4,924,934
Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Unsecured Debt [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	$ 15,944,410		$ 19,401,230

[1] Amounts represent the effect of legally enforceable master netting agreements or other legally enforceable arrangements between the Bank and its derivative counterparties that allow the Bank to offset positive and negative positions as well as the cash collateral held or placed with those same counterparties.