Netting Arrangements (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Assets:
Derivative assets, gross amount	$ 4,295	$ 5,168
Derivative assets, gross amount offset	(4,034)	(4,514)
Derivative assets, net amount presented in our condensed consolidated balance sheets	261	654
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	(154)	(357)
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	(11)	(22)
Derivative assets, net amount	96	275
Securities purchased under agreements to resell or similar arrangements, gross amount	40,490	51,115
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	40,490	51,115
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	(40,490)	(51,115)
Securities purchased under agreements to resell or similar arrangements, net amount	0	0
Total assets, gross amount	44,785	56,283
Total assets, gross amount offset	(4,034)	(4,514)
Total assets, net amount presented in our condensed consolidated balance sheets	40,751	51,769
Total assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	(154)	(357)
Total assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	(40,501)	(51,137)
Total assets, net amount	96	275
Liabilities:
Derivative liabilities, gross amount	(5,213)	(8,057)
Derivative liabilities, gross amount offset	4,877	6,844
Derivative liabilities, net amount presented in our condensed consolidated balance sheets	(336)	(1,213)
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	154	357
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	15	107
Derivative liabilities, net amount	(167)	(749)
Securities sold under agreements to repurchase or similar arrangements, gross amount	(81)
Securities sold under agreements to repurchase or similar arrangements, gross amount offset	0
Securities sold under agreements to repurchase or similar arrangements, net amount presented in our condensed consolidated balance sheets	(81)
Securities sold under agreements to repurchase or similar arrangements, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	0
Securities sold under agreements to repurchase or similar arrangements, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	81
Securities sold under agreements to repurchase or similar arrangements, net amount	0
Total liabilities, gross amount	(5,294)	(8,057)
Total liabilities, gross amount offset	4,877	6,844
Total liabilities, net amount presented in our condensed consolidated balance sheets	(417)	(1,213)
Total liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	154	357
Total liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	96	107
Total liabilities, net amount	(167)	(749)
Risk Management Derivatives
Assets:
Derivative assets, gross amount offset	(4,034)	(4,514)
Liabilities:
Derivative liabilities, gross amount offset	4,877	6,844
Mortgage commitment derivatives
Assets:
Derivative assets, gross amount	221	631
Derivative assets, gross amount offset	0	0
Derivative assets, net amount presented in our condensed consolidated balance sheets	221	631
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	(154)	(357)
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	(11)	(22)
Derivative assets, net amount	56	252
Liabilities:
Derivative liabilities, gross amount	(210)	(737)
Derivative liabilities, gross amount offset	0	0
Derivative liabilities, net amount presented in our condensed consolidated balance sheets	(210)	(737)
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	154	357
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	0	16
Derivative liabilities, net amount	(56)	(364)
Over the Counter [Member] | Risk Management Derivatives
Assets:
Derivative assets, gross amount	2,504	3,688
Derivative assets, gross amount offset	(2,478)	(3,667)
Derivative assets, net amount presented in our condensed consolidated balance sheets	26	21
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	26	21
Liabilities:
Derivative liabilities, gross amount	(3,292)	(4,905)
Derivative liabilities, gross amount offset	3,181	4,520
Derivative liabilities, net amount presented in our condensed consolidated balance sheets	(111)	(385)
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	(111)	(385)
Exchange Cleared [Member] | Risk Management Derivatives
Assets:
Derivative assets, gross amount	1,570	849
Derivative assets, gross amount offset	(1,556)	(847)
Derivative assets, net amount presented in our condensed consolidated balance sheets	14	2
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	14	2
Liabilities:
Derivative liabilities, gross amount	(1,711)	(2,415)
Derivative liabilities, gross amount offset	1,696	2,324
Derivative liabilities, net amount presented in our condensed consolidated balance sheets	(15)	(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	15	91
Derivative liabilities, net amount	$ 0	$ 0