Derivatives and Hedging Activities (Derivatives in Statement of Condition) (Details) - USD ($) $ in Thousands		Sep. 30, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount		$ 22,200,383	$ 46,389,608
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement		7,452	16,201
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		5,329	8,869
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	[1],[2]	153,534	124,050
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	[1],[2]	(3,578)	(5,845)
Derivative assets		160,986	140,251
Derivative liabilities		1,751	3,024
Cash Collateral posted		160,000	138,100
Cash Collateral received		2,900	8,200
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount		19,000,868	34,572,128
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement		5,978	14,079
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		3,124	4,148
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount		3,199,515	11,817,480
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement		1,474	2,122
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		2,205	4,721
Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount		1,926,488	10,413,906
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement		430	1,676
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		2,102	4,642
Not Designated as Hedging Instrument [Member] | Interest Rate Caps or Floors [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount		1,205,000	1,330,000
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement		995	417
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		0	0
Mortgage Receivable [Member] | Not Designated as Hedging Instrument [Member] | Forward Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount		68,027	73,574
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement		49	29
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		$ 103	$ 79

[1] Amounts represent the application of the netting requirements that allow the Bank to settle positive and negative positions, cash collateral and related accrued interest held or placed with the same clearing agent and/or counterparties. Cash collateral posted and related accrued interest was $160.0 million and $138.1 million at September 30, 2020 and December 31, 2019, respectively. Cash collateral received was $2.9 million for September 30, 2020 and $8.2 million for December 31, 2019.

[2] Amounts represent the application of the netting requirements that allow the Bank to settle positive and negative positions and also cash collateral held and related interest accrued or placed by the Bank with the same clearing agent and/or counterparties.