Netting Arrangements (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
Offsetting Assets [Line Items]
Fair Value of Securities Received as Collateral that Have Been Resold or Repledged	$ 0	$ 0	$ 0
Derivative Liability, Not Subject to Master Netting Arrangement	38	38	25
Assets:
Derivative assets, gross amount	2,616	2,616	1,519
Derivative assets, gross amount offset	(2,037)	(2,037)	(1,288)
Derivative assets, net amount presented in our condensed consolidated balance sheets	579	579	231
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	(289)	(289)	(101)
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	(23)	(23)	(1)
Derivative assets, net amount	267	267	129
Securities purchased under agreements to resell or similar arrangements, gross amount	27,100	27,100	24,928
Securities purchased under agreements to resell or similar arrangements, gross amount offset	0	0	0
Securities Purchased under Agreements to Resell, Not Subject to Master Netting Arrangement	27,100	27,100	24,928
Securities purchased under agreements to resell or similar arrangements, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	0	0	0
Securities purchased under agreements to resell or similar arrangements, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	(27,100)	(27,100)	(24,928)
Securities purchased under agreements to resell or similar arrangements, net amount	0	0	0
Total assets, gross amount	29,716	29,716	26,447
Total assets, gross amount offset	(2,037)	(2,037)	(1,288)
Total assets, net amount presented in our condensed consolidated balance sheets	27,679	27,679	25,159
Total assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	(289)	(289)	(101)
Total assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	(27,123)	(27,123)	(24,929)
Total assets, net amount	267	267	129
Liabilities:
Derivative liabilities, gross amount	(2,980)	(2,980)	(2,104)
Derivative liabilities, gross amount offset	2,053	2,053	1,694
Derivative liabilities, net amount presented in our condensed consolidated balance sheets	(927)	(927)	(410)
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	289	289	101
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	532	532	182
Derivative liabilities, net amount	(106)	(106)	(127)
Total liabilities, gross amount	(2,980)	(2,980)	(2,582)
Total liabilities, gross amount offset	2,053	2,053	1,694
Total liabilities, net amount presented in our condensed consolidated balance sheets	(927)	(927)	(888)
Total liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	289	289	101
Total liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	532	532	657
Total liabilities, net amount	(106)	(106)	(130)
Securities Sold under Agreements to Repurchase, Amount Offset Against Collateral			3
Securities Sold under Agreements to Repurchase, Not Subject to Master Netting Arrangement			478
Securities Sold under Agreements to Repurchase, Gross			478
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Securities			475
Single-family [Member]
Liabilities:
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	219	573
Risk Management Derivatives
Assets:
Derivative assets, gross amount offset	(2,037)	(2,037)	(1,288)
Liabilities:
Derivative liabilities, gross amount offset	2,053	2,053	1,694
Mortgage commitment derivatives
Assets:
Derivative assets, gross amount	563	563	165
Derivative assets, gross amount offset	0	0	0
Derivative assets, net amount presented in our condensed consolidated balance sheets	563	563	165
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	(289)	(289)	(101)
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	(23)	(23)	(1)
Derivative assets, net amount	251	251	63
Liabilities:
Derivative liabilities, gross amount	(842)	(842)	(306)
Derivative liabilities, gross amount offset	0	0	0
Derivative liabilities, net amount presented in our condensed consolidated balance sheets	(842)	(842)	(306)
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	289	289	101
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	529	529	181
Derivative liabilities, net amount	(24)	(24)	(24)
Over the Counter [Member] | Risk Management Derivatives
Assets:
Derivative assets, gross amount	2,053	2,053	1,354
Derivative assets, gross amount offset	(2,052)	(2,052)	(1,334)
Derivative assets, net amount presented in our condensed consolidated balance sheets	1	1	20
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	0	0	0
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	0	0	0
Derivative assets, net amount	1	1	20
Liabilities:
Derivative liabilities, gross amount	(2,138)	(2,138)	(1,798)
Derivative liabilities, gross amount offset	2,056	2,056	1,695
Derivative liabilities, net amount presented in our condensed consolidated balance sheets	(82)	(82)	(103)
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	0	0	0
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	0	0	0
Derivative liabilities, net amount	(82)	(82)	(103)
Exchange Cleared [Member] | Risk Management Derivatives
Assets:
Derivative assets, gross amount	0	0	0
Derivative assets, gross amount offset	15	15	46
Derivative assets, net amount presented in our condensed consolidated balance sheets	15	15	46
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	0	0	0
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	0	0	0
Derivative assets, net amount	15	15	46
Liabilities:
Derivative liabilities, gross amount	0	0	0
Derivative liabilities, gross amount offset	(3)	(3)	(1)
Derivative liabilities, net amount presented in our condensed consolidated balance sheets	(3)	(3)	(1)
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	0	0	0
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	3	3	1
Derivative liabilities, net amount	$ 0	$ 0	$ 0