Netting Arrangements (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Offsetting Assets [Line Items]
Financial Instruments Owned and Pledged as Collateral, Amount Eligible to be Repledged by Counterparty	$ 1,900	$ 747
Assets:
Derivative assets, gross amount	2,667	4,422
Derivative asset, gross amount offset	(2,266)	(4,272)
Derivative assets, net amount presented in our consolidated balance sheets	401	150
Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments	(153)	(117)
Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	(7)	(1)
Derivative assets, net amount	241	32
Securities purchased under agreements to resell, or similar arrangements, gross amount	48,288	44,670
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	48,288	44,670
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	(48,288)	(44,670)
Securities purchased under agreements to resell or similar arrangements, net amount	0	0
Total assets, gross amount	50,955	49,092
Total assets, gross amount offset	(2,266)	(4,272)
Total assets, net amount presented in the consolidated balance sheets	48,689	44,820
Total assets, under the master netting arrangements, not offset in our consolidated balance sheets, financial instruments	(153)	(117)
Total assets, under master netting arrangements, not offset in our consolidated balance sheets, collateral	(48,295)	(44,671)
Total assets, net amount	241	32
Liabilities:
Derivative liabilities, gross amount	(3,081)	(5,306)
Derivative liabilities, gross amount offset	2,315	4,979
Derivative liabilities, net amount presented in our consolidated balance sheets	(766)	(327)
Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments	153	117
Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	489	104
Derivative liabilities, net amount	(124)	(106)
Total liabilities, gross amount	(3,081)	(5,306)
Total liabilities, gross amount offset	2,315	4,979
Total liabilities, net amount presented in our consolidated balance sheets	(766)	(327)
Total liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial statements	153	117
Total liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	489	104
Total liabilities, net amount	(124)	(106)
Securities Received as Collateral	48,400	44,700
Fair Value of Securities Received as Collateral that Can be Resold or Repledged	45,700	42,500
Fair Value of Securities Received as Collateral that Have Been Resold or Repledged	0	0
Derivative Asset, Not Subject to Master Netting Arrangement	57	21
Derivative Liability, Not Subject to Master Netting Arrangement	11	1
Risk management derivatives
Assets:
Derivative asset, gross amount offset	(2,266)	(4,272)
Liabilities:
Derivative liabilities, gross amount offset	2,315	4,979
Mortgage commitment derivatives
Assets:
Derivative assets, gross amount	379	132
Derivative asset, gross amount offset	0	0
Derivative assets, net amount presented in our consolidated balance sheets	379	132
Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments	(153)	(117)
Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	(7)	(1)
Derivative assets, net amount	219	14
Liabilities:
Derivative liabilities, gross amount	(648)	(228)
Derivative liabilities, gross amount offset	0	0
Derivative liabilities, net amount presented in our consolidated balance sheets	(648)	(228)
Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments	153	117
Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	466	93
Derivative liabilities, net amount	(29)	(18)
Over the Counter [Member] | Risk management derivatives
Assets:
Derivative assets, gross amount	2,288	2,479
Derivative asset, gross amount offset	(2,273)	(2,464)
Derivative assets, net amount presented in our consolidated balance sheets	15	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	15	15
Liabilities:
Derivative liabilities, gross amount	(2,433)	(3,045)
Derivative liabilities, gross amount offset	2,342	2,957
Derivative liabilities, net amount presented in our consolidated balance sheets	(91)	(88)
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	(91)	(88)
Exchange Cleared [Member] | Risk management derivatives
Assets:
Derivative assets, gross amount	0	1,811
Derivative asset, gross amount offset	7	(1,808)
Derivative assets, net amount presented in our consolidated balance sheets	7	3
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	7	3
Liabilities:
Derivative liabilities, gross amount	0	(2,033)
Derivative liabilities, gross amount offset	(27)	2,022
Derivative liabilities, net amount presented in our consolidated balance sheets	(27)	(11)
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	23	11
Derivative liabilities, net amount	(4)	0
Cash and Cash Equivalents [Member]
Liabilities:
Securities Purchased under Agreements to Resell	$ 15,400	$ 25,200