Netting Arrangements (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Offsetting Assets [Line Items]
Financial Instruments Owned and Pledged as Collateral, Amount Eligible to be Repledged by Counterparty	$ 4,700	$ 2,300
Assets:
Derivative assets, gross amount	1,951	1,519
Derivative asset, gross amount offset	(905)	(1,288)
Derivative assets, net amount presented in our consolidated balance sheets	1,046	231
Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments	(406)	(101)
Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	(53)	(1)
Derivative assets, net amount	587	129
Securities purchased under agreements to resell, or similar arrangements, gross amount	46,644	24,928
Securities purchased under agreements to resell or similar arrangements, gross amount offset	0	0
Securities purchased under agreements to resell or similar arrangements, net amount presented in our consolidated balance sheets	46,644	24,928
Securities purchased under agreements to resell, under master netting arrangement, amounts not offset in our 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 consolidated balance sheets, collateral	(46,644)	(24,928)
Securities purchased under agreements to resell or similar arrangements, net amount	0	0
Total assets, gross amount	48,595	26,447
Total assets, gross amount offset	(905)	(1,288)
Total assets, net amount presented in the consolidated balance sheets	47,690	25,159
Total assets, under the master netting arrangements, not offset in our consolidated balance sheets, financial instruments	(406)	(101)
Total assets, under master netting arrangements, not offset in our consolidated balance sheets, collateral	(46,697)	(24,929)
Total assets, net amount	587	129
Liabilities:
Derivative liabilities, gross amount	(2,441)	(2,104)
Derivative liabilities, gross amount offset	995	1,694
Derivative liabilities, net amount presented in our consolidated balance sheets	(1,446)	(410)
Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments	406	101
Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	1,019	182
Derivative liabilities, net amount	(21)	(127)
Securities Sold under Agreements to Repurchase, Gross		(478)
Securities Sold under Agreements to Repurchase, Not Subject to Master Netting Arrangement		(478)
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Securities		475
Securities Sold under Agreements to Repurchase, Amount Offset Against Collateral		(3)
Total liabilities, gross amount	(2,441)	(2,582)
Total liabilities, gross amount offset	995	1,694
Total liabilities, net amount presented in our consolidated balance sheets	(1,446)	(888)
Total liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial statements	406	101
Total liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	1,019	657
Total liabilities, net amount	(21)	(130)
Securities Received as Collateral	46,600	24,700
Fair Value of Securities Received as Collateral that Can be Resold or Repledged	46,600	23,800
Fair Value of Securities Received as Collateral that Have Been Resold or Repledged	0	0
Derivative Asset, Not Subject to Master Netting Arrangement	179	40
Derivative Liability, Not Subject to Master Netting Arrangement	49	25
Risk management derivatives
Assets:
Derivative asset, gross amount offset	(905)	(1,288)
Liabilities:
Derivative liabilities, gross amount offset	995	1,694
Mortgage commitment derivatives
Assets:
Derivative assets, gross amount	989	165
Derivative asset, gross amount offset	0	0
Derivative assets, net amount presented in our consolidated balance sheets	989	165
Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments	(406)	(101)
Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	(53)	(1)
Derivative assets, net amount	530	63
Liabilities:
Derivative liabilities, gross amount	(1,426)	(306)
Derivative liabilities, gross amount offset	0	0
Derivative liabilities, net amount presented in our consolidated balance sheets	(1,426)	(306)
Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments	406	101
Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	1,017	181
Derivative liabilities, net amount	(3)	(24)
Over the Counter [Member] | Risk management derivatives
Assets:
Derivative assets, gross amount	962	1,354
Derivative asset, gross amount offset	(952)	(1,334)
Derivative assets, net amount presented in our consolidated balance sheets	10	20
Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments	0	0
Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	0	0
Derivative assets, net amount	10	20
Liabilities:
Derivative liabilities, gross amount	(1,015)	(1,798)
Derivative liabilities, gross amount offset	999	1,695
Derivative liabilities, net amount presented in our consolidated balance sheets	(16)	(103)
Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments	0	0
Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	0	0
Derivative liabilities, net amount	(16)	(103)
Exchange Cleared [Member] | Risk management derivatives
Assets:
Derivative assets, gross amount	0	0
Derivative asset, gross amount offset	47	46
Derivative assets, net amount presented in our consolidated balance sheets	47	46
Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments	0	0
Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	0	0
Derivative assets, net amount	47	46
Liabilities:
Derivative liabilities, gross amount	0	0
Derivative liabilities, gross amount offset	(4)	(1)
Derivative liabilities, net amount presented in our consolidated balance sheets	(4)	(1)
Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments	0	0
Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	2	1
Derivative liabilities, net amount	(2)	0
Cash and Cash Equivalents [Member]
Liabilities:
Securities Purchased under Agreements to Resell	$ 18,400	$ 11,400