Netting Arrangements (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
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	27	11
Assets:
Derivative assets, gross amount	2,093	2,667
Derivative assets, gross amount offset	(1,663)	(2,266)
Derivative assets, net amount presented in our condensed consolidated balance sheets	430	401
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	(368)	(153)
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	(7)	(7)
Derivative assets, net amount	55	241
Securities purchased under agreements to resell or similar arrangements, gross amount	36,051	48,288
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	36,051	48,288
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	(36,051)	(48,288)
Securities purchased under agreements to resell or similar arrangements, net amount	0	0
Total assets, gross amount	38,144	50,955
Total assets, gross amount offset	(1,663)	(2,266)
Total assets, net amount presented in our condensed consolidated balance sheets	36,481	48,689
Total assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	(368)	(153)
Total assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	(36,058)	(48,295)
Total assets, net amount	55	241
Liabilities:
Derivative liabilities, gross amount	(2,867)	(3,081)
Derivative liabilities, gross amount offset	2,299	2,315
Derivative liabilities, net amount presented in our condensed consolidated balance sheets	(568)	(766)
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	368	153
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	37	489
Derivative liabilities, net amount	(163)	(124)
Total liabilities, gross amount	(3,992)	(3,081)
Total liabilities, gross amount offset	2,299	2,315
Total liabilities, net amount presented in our condensed consolidated balance sheets	(1,693)	(766)
Total liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	368	153
Total liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	1,160	489
Total liabilities, net amount	(165)	(124)
Fair Value of Securities Received as Collateral that Can be Resold or Repledged	34,300	45,700
Securities Sold under Agreements to Repurchase, Gross	(1,125)
Securities Sold under Agreements to Repurchase, Asset	0
Securities Sold under Agreements to Repurchase, Not Subject to Master Netting Arrangement	(1,125)
Securities Sold under Agreements to Repurchase, Not Offset, Policy Election Deduction	0
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Securities	1,123
Securities Sold under Agreements to Repurchase, Amount Offset Against Collateral	2
Risk Management Derivatives
Assets:
Derivative assets, gross amount offset	(1,663)	(2,266)
Liabilities:
Derivative liabilities, gross amount offset	2,299	2,315
Mortgage commitment derivatives
Assets:
Derivative assets, gross amount	421	379
Derivative assets, gross amount offset	0	0
Derivative assets, net amount presented in our condensed consolidated balance sheets	421	379
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	(368)	(153)
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	(7)	(7)
Derivative assets, net amount	46	219
Liabilities:
Derivative liabilities, gross amount	(416)	(648)
Derivative liabilities, gross amount offset	0	0
Derivative liabilities, net amount presented in our condensed consolidated balance sheets	(416)	(648)
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	368	153
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	4	466
Derivative liabilities, net amount	(44)	(29)
Over the Counter [Member] | Risk Management Derivatives
Assets:
Derivative assets, gross amount	1,672	2,288
Derivative assets, gross amount offset	(1,667)	(2,273)
Derivative assets, net amount presented in our condensed consolidated balance sheets	5	15
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	5	15
Liabilities:
Derivative liabilities, gross amount	(2,451)	(2,433)
Derivative liabilities, gross amount offset	2,332	2,342
Derivative liabilities, net amount presented in our condensed consolidated balance sheets	(119)	(91)
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	(119)	(91)
Exchange Cleared [Member] | Risk Management Derivatives
Assets:
Derivative assets, gross amount	0	0
Derivative assets, gross amount offset	4	7
Derivative assets, net amount presented in our condensed consolidated balance sheets	4	7
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	7
Liabilities:
Derivative liabilities, gross amount	0	0
Derivative liabilities, gross amount offset	(33)	(27)
Derivative liabilities, net amount presented in our condensed consolidated balance sheets	(33)	(27)
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	33	23
Derivative liabilities, net amount	$ 0	$ (4)