Fair Value (Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	$ 888	$ 915
Available-for-Sale Securities	16,651	19,019
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	63	(46)
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	201	130
Derivative Asset, Net	102	58
Derivative Liability, Net	(1)	(9)
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	0	0
Available-for-Sale Securities	0	0
Derivative Asset, Net	0	0
Other Assets, Fair Value Disclosure	34	27
Derivative Liability, Net	0	0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	888	915
Available-for-Sale Securities	16,651	19,019
Derivative Asset, Net	39	104
Other Assets, Fair Value Disclosure	0	0
Derivative Liability, Net	(202)	(139)
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	0	0
Available-for-Sale Securities	0	0
Derivative Asset, Net	0	0
Other Assets, Fair Value Disclosure	0	0
Derivative Liability, Net	0	0
Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	63	(46)
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	201	130
Fair Value, 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
Available-for-Sale Securities	0	0
Financial and Nonfinancial Liabilities, Fair Value Disclosure	0	0
Derivative Asset, Net		0
Other Assets, Fair Value Disclosure	34	27
Assets, Fair Value Disclosure	34	27
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	888	915
Available-for-Sale Securities	16,651	19,019
Financial and Nonfinancial Liabilities, Fair Value Disclosure	(202)	(139)
Derivative Asset, Net		104
Other Assets, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	17,578	20,038
Fair Value, 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
Available-for-Sale Securities	0	0
Financial and Nonfinancial Liabilities, Fair Value Disclosure	0	0
Derivative Asset, Net		0
Other Assets, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	0	0
Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	888	915
Available-for-Sale Securities	16,651	19,019
Derivative Asset, Net	102	58
Other Assets, Fair Value Disclosure	34	27
Derivative Liability, Net	(1)	(9)
Estimate of Fair Value Measurement [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	888	915
Available-for-Sale Securities	16,651	19,019
Financial and Nonfinancial Liabilities, Fair Value Disclosure	(1)	(9)
Derivative Asset, Net		58
Other Assets, Fair Value Disclosure	34	27
Assets, Fair Value Disclosure	17,675	20,019
Interest Rate Swap [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	63	(46)
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	201	130
Interest Rate Swap [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Net	0	0
Derivative Liability, Net	0	0
Interest Rate Swap [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Net	39	103
Derivative Liability, Net	(202)	(139)
Interest Rate Swap [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Net	0	0
Derivative Liability, Net	0	0
Interest Rate Swap [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Net	102	57
Derivative Liability, Net	(1)	(9)
U.S. Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	150	159
Available-for-Sale Securities	2,127	2,602
U.S. Obligations [Member] | Fair Value, 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
Available-for-Sale Securities	0	0
U.S. Obligations [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	150	159
Available-for-Sale Securities	2,127	2,602
U.S. Obligations [Member] | Fair Value, 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
Available-for-Sale Securities	0	0
U.S. Obligations [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	150	159
Available-for-Sale Securities	2,127	2,602
GSE Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	60	57
Available-for-Sale Securities	1,060	1,038
GSE Obligations [Member] | Fair Value, 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
Available-for-Sale Securities	0	0
GSE Obligations [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	60	57
Available-for-Sale Securities	1,060	1,038
GSE Obligations [Member] | Fair Value, 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
Available-for-Sale Securities	0	0
GSE Obligations [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	60	57
Available-for-Sale Securities	1,060	1,038
State or Local Housing Agency Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	756	814
State or Local Housing Agency Obligations [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
State or Local Housing Agency Obligations [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	756	814
State or Local Housing Agency Obligations [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
State or Local Housing Agency Obligations [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	756	814
Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	259	266
Available-for-Sale Securities	285	275
Other [Member] | Fair Value, 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
Available-for-Sale Securities	0	0
Other [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	259	266
Available-for-Sale Securities	285	275
Other [Member] | Fair Value, 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
Available-for-Sale Securities	0	0
Other [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	259	266
Available-for-Sale Securities	285	275
U.S. Obligations MBS [Member] | Single Family [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	4,059	4,483
U.S. Obligations MBS [Member] | Single Family [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
U.S. Obligations MBS [Member] | Single Family [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	4,059	4,483
U.S. Obligations MBS [Member] | Single Family [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
U.S. Obligations MBS [Member] | Single Family [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	4,059	4,483
GSE MBS [Member] | Single Family [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	649	796
GSE MBS [Member] | Single Family [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
GSE MBS [Member] | Single Family [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	649	796
GSE MBS [Member] | Single Family [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	0	0
GSE MBS [Member] | Single Family [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-Sale Securities	649	796
GSE MBS [Member] | Multifamily [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	419	433
Available-for-Sale Securities	7,715	9,011
GSE MBS [Member] | Multifamily [Member] | Fair Value, 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
Available-for-Sale Securities	0	0
GSE MBS [Member] | Multifamily [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	419	433
Available-for-Sale Securities	7,715	9,011
GSE MBS [Member] | Multifamily [Member] | Fair Value, 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
Available-for-Sale Securities	0	0
GSE MBS [Member] | Multifamily [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	419	433
Available-for-Sale Securities	$ 7,715	9,011
Mortgage Receivable [Member] | Forward Contracts [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Net		0
Mortgage Receivable [Member] | Forward Contracts [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Net		1
Mortgage Receivable [Member] | Forward Contracts [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Net		0
Mortgage Receivable [Member] | Forward Contracts [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Net		$ 1