Netting Arrangements (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Offsetting Assets [Line Items]
Financial Instruments Owned and Pledged as Collateral, Amount Eligible to be Repledged by Counterparty	$ 2,300	$ 1,900
Assets:
Derivative assets, gross amount	1,519	2,667
Derivative asset, gross amount offset	(1,288)	(2,266)
Derivative assets, net amount presented in our consolidated balance sheets	231	401
Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments	(101)	(153)
Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	(1)	(7)
Derivative assets, net amount	129	241
Securities purchased under agreements to resell, or similar arrangements, gross amount	24,928	48,288
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	24,928	48,288
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	(24,928)	(48,288)
Securities purchased under agreements to resell or similar arrangements, net amount	0	0
Total assets, gross amount	26,447	50,955
Total assets, gross amount offset	(1,288)	(2,266)
Total assets, net amount presented in the consolidated balance sheets	25,159	48,689
Total assets, under the master netting arrangements, not offset in our consolidated balance sheets, financial instruments	(101)	(153)
Total assets, under master netting arrangements, not offset in our consolidated balance sheets, collateral	(24,929)	(48,295)
Total assets, net amount	129	241
Liabilities:
Derivative liabilities, gross amount	(2,104)	(3,081)
Derivative liabilities, gross amount offset	1,694	2,315
Derivative liabilities, net amount presented in our consolidated balance sheets	(410)	(766)
Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments	101	153
Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	182	489
Derivative liabilities, net amount	(127)	(124)
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	(2,582)	(3,081)
Total liabilities, gross amount offset	1,694	2,315
Total liabilities, net amount presented in our consolidated balance sheets	(888)	(766)
Total liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial statements	101	153
Total liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	657	489
Total liabilities, net amount	(130)	(124)
Securities Received as Collateral	24,700	48,400
Fair Value of Securities Received as Collateral that Can be Resold or Repledged	23,800	45,700
Fair Value of Securities Received as Collateral that Have Been Resold or Repledged	0	0
Derivative Asset, Not Subject to Master Netting Arrangement	40	57
Derivative Liability, Not Subject to Master Netting Arrangement	25	11
Risk management derivatives
Assets:
Derivative asset, gross amount offset	(1,288)	(2,266)
Liabilities:
Derivative liabilities, gross amount offset	1,694	2,315
Mortgage commitment derivatives
Assets:
Derivative assets, gross amount	165	379
Derivative asset, gross amount offset	0	0
Derivative assets, net amount presented in our consolidated balance sheets	165	379
Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments	(101)	(153)
Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	(1)	(7)
Derivative assets, net amount	63	219
Liabilities:
Derivative liabilities, gross amount	(306)	(648)
Derivative liabilities, gross amount offset	0	0
Derivative liabilities, net amount presented in our consolidated balance sheets	(306)	(648)
Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments	101	153
Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	181	466
Derivative liabilities, net amount	(24)	(29)
Over the Counter [Member] | Risk management derivatives
Assets:
Derivative assets, gross amount	1,354	2,288
Derivative asset, gross amount offset	(1,334)	(2,273)
Derivative assets, net amount presented in our consolidated balance sheets	20	15
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	20	15
Liabilities:
Derivative liabilities, gross amount	(1,798)	(2,433)
Derivative liabilities, gross amount offset	1,695	2,342
Derivative liabilities, net amount presented in our consolidated balance sheets	(103)	(91)
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	(103)	(91)
Exchange Cleared [Member] | Risk management derivatives
Assets:
Derivative assets, gross amount	0	0
Derivative asset, gross amount offset	46	7
Derivative assets, net amount presented in our consolidated balance sheets	46	7
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	46	7
Liabilities:
Derivative liabilities, gross amount	0	0
Derivative liabilities, gross amount offset	(1)	(27)
Derivative liabilities, net amount presented in our consolidated balance sheets	(1)	(27)
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	1	23
Derivative liabilities, net amount	0	(4)
Cash and Cash Equivalents [Member]
Liabilities:
Securities Purchased under Agreements to Resell	$ 11,400	$ 15,400