Netting Arrangements (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Offsetting Assets [Line Items]
Fair Value of Securities Received as Collateral that Have Been Resold or Repledged	$ 0	$ 0
Derivative Liability, Not Subject to Master Netting Arrangement	29	25
Assets:
Derivative assets, gross amount	4,871	1,519
Derivative assets, gross amount offset	(2,137)	(1,288)
Derivative assets, net amount presented in our condensed consolidated balance sheets	2,734	231
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	(1,228)	(101)
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	(499)	(1)
Derivative assets, net amount	1,007	129
Securities purchased under agreements to resell or similar arrangements, gross amount	20,175	24,928
Securities purchased under agreements to resell or similar arrangements, gross amount offset	0	0
Securities Purchased under Agreements to Resell, Not Subject to Master Netting Arrangement	20,175	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
Securities purchased under agreements to resell or similar arrangements, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	(20,175)	(24,928)
Securities purchased under agreements to resell or similar arrangements, net amount	0	0
Total assets, gross amount	25,046	26,447
Total assets, gross amount offset	(2,137)	(1,288)
Total assets, net amount presented in our condensed consolidated balance sheets	22,909	25,159
Total assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	(1,228)	(101)
Total assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	(20,674)	(24,929)
Total assets, net amount	1,007	129
Liabilities:
Derivative liabilities, gross amount	(6,387)	(2,104)
Derivative liabilities, gross amount offset	2,607	1,694
Derivative liabilities, net amount presented in our condensed consolidated balance sheets	(3,780)	(410)
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	1,228	101
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	2,385	182
Derivative liabilities, net amount	(167)	(127)
Total liabilities, gross amount	(6,387)	(2,582)
Total liabilities, gross amount offset	2,607	1,694
Total liabilities, net amount presented in our condensed consolidated balance sheets	(3,780)	(888)
Total liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	1,228	101
Total liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	2,385	657
Total liabilities, net amount	(167)	(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	182
Risk Management Derivatives
Assets:
Derivative assets, gross amount offset	(2,137)	(1,288)
Liabilities:
Derivative liabilities, gross amount offset	2,607	1,694
Mortgage commitment derivatives
Assets:
Derivative assets, gross amount	2,665	165
Derivative assets, gross amount offset	0	0
Derivative assets, net amount presented in our condensed consolidated balance sheets	2,665	165
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	(1,228)	(101)
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	(499)	(1)
Derivative assets, net amount	938	63
Liabilities:
Derivative liabilities, gross amount	(3,594)	(306)
Derivative liabilities, gross amount offset	0	0
Derivative liabilities, net amount presented in our condensed consolidated balance sheets	(3,594)	(306)
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	1,228	101
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	2,349	181
Derivative liabilities, net amount	(17)	(24)
Over the Counter [Member] | Risk Management Derivatives
Assets:
Derivative assets, gross amount	2,206	1,354
Derivative assets, gross amount offset	(2,202)	(1,334)
Derivative assets, net amount presented in our condensed consolidated balance sheets	4	20
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	0	0
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	0	0
Derivative assets, net amount	4	20
Liabilities:
Derivative liabilities, gross amount	(2,793)	(1,798)
Derivative liabilities, gross amount offset	2,643	1,695
Derivative liabilities, net amount presented in our condensed consolidated balance sheets	(150)	(103)
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	0	0
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	0	0
Derivative liabilities, net amount	(150)	(103)
Exchange Cleared [Member] | Risk Management Derivatives
Assets:
Derivative assets, gross amount	0	0
Derivative assets, gross amount offset	65	46
Derivative assets, net amount presented in our condensed consolidated balance sheets	65	46
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	0	0
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	0	0
Derivative assets, net amount	65	46
Liabilities:
Derivative liabilities, gross amount	0	0
Derivative liabilities, gross amount offset	(36)	(1)
Derivative liabilities, net amount presented in our condensed consolidated balance sheets	(36)	(1)
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	0	0
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	36	1
Derivative liabilities, net amount	$ 0	$ 0