Commitments and Contingencies Off-Balance Sheet Commitments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Loss Contingencies [Line Items]
Obligation with Joint and Several Liability Arrangement, Amount Outstanding	$ 1,025,895	$ 1,031,617
Standby Letters Of Credit, Final Expiration	2034
Other Liabilities	$ 362	252
Commitments to purchase mortgage loans, maximum term	60 days
Total consolidated obligations, par value	$ 98,817	101,609
Assets Pledged As Collateral	759
Security Owned and Pledged as Collateral, Fair Value	381
Derivative, Collateral, Right to Reclaim Cash	378	257
Standby letters of credit outstanding
Loss Contingencies [Line Items]
Expire Within One Year	16,898	13,661
Expire After One Year	4,658	4,418
Total	21,556	18,079
Other Liabilities	32	27
Commitments to issue consolidated obligation discount notes, par
Loss Contingencies [Line Items]
Expire Within One Year	805	350
Expire After One Year	0	0
Total	$ 805	350
Minimum | Standby letters of credit outstanding
Loss Contingencies [Line Items]
Guarantor Obligations, Term	3 days
Maximum | Standby letters of credit outstanding
Loss Contingencies [Line Items]
Guarantor Obligations, Term	15 years
Guarantee of Indebtedness of Others
Loss Contingencies [Line Items]
Total consolidated obligations, par value	$ 98,817	101,609
Mortgages | Commitments to purchase mortgage loans
Loss Contingencies [Line Items]
Expire Within One Year	46	12
Expire After One Year	0	0
Total	$ 46	$ 12