Netting Arrangements (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Assets:
Derivative assets, gross amount	$ 4,420	$ 5,168
Derivative assets, gross amount offset	(4,024)	(4,514)
Derivative assets, net amount presented in our condensed consolidated balance sheets	396	654
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	(234)	(357)
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	0	(22)
Derivative assets, net amount	162	275
Securities purchased under agreements to resell or similar arrangements, gross amount	41,120	51,115
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 condensed consolidated balance sheets	41,120	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	(41,120)	(51,115)
Securities purchased under agreements to resell or similar arrangements, net amount	0	0
Total assets, gross amount	45,540	56,283
Total assets, gross amount offset	(4,024)	(4,514)
Total assets, net amount presented in our condensed consolidated balance sheets	41,516	51,769
Total assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	(234)	(357)
Total assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	(41,120)	(51,137)
Total assets, net amount	162	275
Liabilities:
Derivative liabilities, gross amount	(5,453)	(8,057)
Derivative liabilities, gross amount offset	5,034	6,844
Derivative liabilities, net amount presented in our condensed consolidated balance sheets	(419)	(1,213)
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	234	357
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	2	107
Derivative liabilities, net amount	(183)	(749)
Securities sold under agreements to repurchase or similar arrangements, gross amount	(7)
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	(7)
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	7
Securities sold under agreements to repurchase or similar arrangements, net amount	0
Total liabilities, gross amount	(5,460)	(8,057)
Total liabilities, gross amount offset	5,034	6,844
Total liabilities, net amount presented in our condensed consolidated balance sheets	(426)	(1,213)
Total liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	234	357
Total liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	9	107
Total liabilities, net amount	(183)	(749)
Risk Management Derivatives [Member]
Assets:
Derivative assets, gross amount offset	(4,024)	(4,514)
Liabilities:
Derivative liabilities, gross amount offset	5,034	6,844
Mortgage commitment derivatives [Member]
Assets:
Derivative assets, gross amount	313	631
Derivative assets, gross amount offset	0	0
Derivative assets, net amount presented in our condensed consolidated balance sheets	313	631
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	(234)	(357)
Derivative assets, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	0	(22)
Derivative assets, net amount	79	252
Liabilities:
Derivative liabilities, gross amount	(318)	(737)
Derivative liabilities, gross amount offset	0	0
Derivative liabilities, net amount presented in our condensed consolidated balance sheets	(318)	(737)
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, financial instruments	234	357
Derivative liabilities, under master netting arrangements, amounts not offset in our condensed consolidated balance sheets, collateral	0	16
Derivative liabilities, net amount	(84)	(364)
Over the Counter [Member] | Risk Management Derivatives [Member]
Assets:
Derivative assets, gross amount	2,800	3,688
Derivative assets, gross amount offset	(2,753)	(3,667)
Derivative assets, net amount presented in our condensed consolidated balance sheets	47	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	47	21
Liabilities:
Derivative liabilities, gross amount	(3,564)	(4,905)
Derivative liabilities, gross amount offset	3,465	4,520
Derivative liabilities, net amount presented in our condensed consolidated balance sheets	(99)	(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	(99)	(385)
Exchange Cleared [Member] | Risk Management Derivatives [Member]
Assets:
Derivative assets, gross amount	1,307	849
Derivative assets, gross amount offset	(1,271)	(847)
Derivative assets, net amount presented in our condensed consolidated balance sheets	36	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	36	2
Liabilities:
Derivative liabilities, gross amount	(1,571)	(2,415)
Derivative liabilities, gross amount offset	1,569	2,324
Derivative liabilities, net amount presented in our condensed consolidated balance sheets	(2)	(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	2	91
Derivative liabilities, net amount	$ 0	$ 0