Netting Arrangements (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
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	46		49
Assets:
Derivative assets, gross amount	3,266		1,951
Derivative assets, gross amount offset	(655)		(905)
Derivative assets, net amount presented in our condensed consolidated balance sheets	2,611		1,046
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	(801)		(406)
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	(85)		(53)
Derivative assets, net amount	1,725		587
Securities purchased under agreements to resell or similar arrangements, gross amount	66,437		46,644
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	66,437		46,644
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	(66,437)		(46,644)
Securities purchased under agreements to resell or similar arrangements, net amount	0		0
Total assets, gross amount	69,703		48,595
Total assets, gross amount offset	(655)		(905)
Total assets, net amount presented in our condensed consolidated balance sheets	69,048		47,690
Total assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	(801)		(406)
Total assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	(66,522)		(46,697)
Total assets, net amount	1,725		587
Liabilities:
Derivative liabilities, gross amount	(3,692)		(2,441)
Derivative liabilities, gross amount offset	1,632		995
Derivative liabilities, net amount presented in our condensed consolidated balance sheets	(2,060)		(1,446)
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	801		406
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	173		1,019
Derivative liabilities, net amount	(1,086)		(21)
Total liabilities, gross amount	(3,692)		(2,441)
Total liabilities, gross amount offset	1,632		995
Total liabilities, net amount presented in our condensed consolidated balance sheets	(2,060)		(1,446)
Total liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	801		406
Total liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	173		1,019
Total liabilities, net amount	(1,086)		(21)
Fair value of non-cash collateral we pledged	4,700		4,700
Cash and Cash Equivalents [Member]
Liabilities:
Securities purchased under agreements to resell	6,100		18,400
Restricted Cash and Cash Equivalent
Liabilities:
Securities purchased under agreements to resell	5,400
Single-family [Member]
Liabilities:
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	307	$ 182
Risk Management Derivatives
Assets:
Derivative assets, gross amount offset	(655)		(905)
Liabilities:
Derivative liabilities, gross amount offset	1,632		995
Mortgage commitment derivatives
Assets:
Derivative assets, gross amount	2,596		989
Derivative assets, gross amount offset	0		0
Derivative assets, net amount presented in our condensed consolidated balance sheets	2,596		989
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	(801)		(406)
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	(85)		(53)
Derivative assets, net amount	1,710		530
Liabilities:
Derivative liabilities, gross amount	(1,972)		(1,426)
Derivative liabilities, gross amount offset	0		0
Derivative liabilities, net amount presented in our condensed consolidated balance sheets	(1,972)		(1,426)
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	801		406
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	159		1,017
Derivative liabilities, net amount	(1,012)		(3)
Over the Counter [Member] | Risk Management Derivatives
Assets:
Derivative assets, gross amount	670		962
Derivative assets, gross amount offset	(661)		(952)
Derivative assets, net amount presented in our condensed consolidated balance sheets	9		10
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	9		10
Liabilities:
Derivative liabilities, gross amount	(1,720)		(1,015)
Derivative liabilities, gross amount offset	1,646		999
Derivative liabilities, net amount presented in our condensed consolidated balance sheets	(74)		(16)
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	(74)		(16)
Exchange Cleared [Member] | Risk Management Derivatives
Assets:
Derivative assets, gross amount	0		0
Derivative assets, gross amount offset	6		47
Derivative assets, net amount presented in our condensed consolidated balance sheets	6		47
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	6		47
Liabilities:
Derivative liabilities, gross amount	0		0
Derivative liabilities, gross amount offset	(14)		(4)
Derivative liabilities, net amount presented in our condensed consolidated balance sheets	(14)		(4)
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	14		2
Derivative liabilities, net amount	$ 0		$ (2)