Netting Arrangements (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Assets
Derivative assets, gross amount	$ 6,621	$ 4,890
Derivative assets, gross amount offset	(6,154)	(4,024)
Derivative assets, net amount presented in the condensed consolidated balance sheets	467	866
Derivative assets, under master netting arrangements, amounts not offset in the condensed consolidated balance sheets, financial instruments	(214)	(119)
Derivative assets, under master netting arrangements, amounts not offset in the condensed consolidated balance sheets, collateral	0	(21)
Derivative assets, net amount	253	726
Securities purchased under agreements to resell or similar arrangements, gross amount	40,600	37,950
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 the condensed consolidated balance sheets	40,600	37,950
Securities purchased under agreements to resell, under master netting arrangement, amounts not offset in the 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 the condensed consolidated balance sheets, collateral	(40,600)	(37,950)
Securities purchased under agreements to resell or similar arrangements, net amount	0	0
Total assets, gross amount	47,221	42,840
Total assets, gross amount offset	(6,154)	(4,024)
Total assets, net amount presented in the condensed consolidated balance sheets	41,067	38,816
Total assets, under master netting arrangements, not offset in the condensed consolidated balance sheets, financial instruments	(214)	(119)
Total assets, under master netting arrangements, not offset in the condensed consolidated balance sheets, collateral	(40,600)	(37,971)
Total assets, net amount	253	726
Liabilities:
Derivative liabilities, gross amount	(13,124)	(9,072)
Derivative liabilities, gross amount offset	12,423	8,650
Derivative liabilities, net amount presented in the condensed consolidated balance sheets	(701)	(422)
Derivative Liability, under master netting arrangements, amounts not offset in the condensed consolidated balance sheets, financial instruments	214	119
Derivative liabilities, under master netting arrangements, amounts not offset in the condensed consolidated balance sheets, collateral	6	(1)
Derivative liabilities, net amount	(481)	(304)
Securities sold under agreements to repurchase or similar arrangements, gross amount	(35)	(62)
Securities sold under agreements to repurchase or similar arrangements, gross amount offset	0	0
Securities sold under agreements to repurchase or similar arrangements, net amount presented in the condensed consolidated balance sheets	(35)	(62)
Securities sold under agreements to repurchase or similar arrangements, under master netting arrangements, amounts not offset in the condensed consolidated balance sheets, financial instruments	0	0
Securities sold under agreements to repurchase or similar arrangements, under master netting arrangements, amounts not offset in the condensed consolidated balance sheets, collateral	35	62
Securities sold under agreements to repurchase or similar arrangements, net amount	0	0
Total liabilities, gross amount	(13,159)	(9,134)
Total liabilities, gross amount offset	12,423	8,650
Total liabilities, net amount presented in the condensed consolidated balance sheets	(736)	(484)
Total liabilities, under master netting arrangements, amounts not offset in the condensed consolidated balance sheets, financial instruments	214	119
Total liabilities, under master netting arrangements, amounts not offset in the condensed consolidated balance sheets, collateral	41	61
Total liabilities, net amount	(481)	(304)
Risk Management Derivatives [Member]
Assets
Derivative assets, gross amount offset	(6,154)	(4,024)
Liabilities:
Derivative liabilities, gross amount offset	12,423	8,650
Mortgage commitment derivatives [Member]
Assets
Derivative assets, gross amount	349	140
Derivative assets, gross amount offset	0	0
Derivative assets, net amount presented in the condensed consolidated balance sheets	349	140
Derivative assets, under master netting arrangements, amounts not offset in the condensed consolidated balance sheets, financial instruments	(214)	(119)
Derivative assets, under master netting arrangements, amounts not offset in the condensed consolidated balance sheets, collateral	0	(3)
Derivative assets, net amount	135	18
Liabilities:
Derivative liabilities, gross amount	(537)	(158)
Derivative liabilities, gross amount offset	0	0
Derivative liabilities, net amount presented in the condensed consolidated balance sheets	(537)	(158)
Derivative Liability, under master netting arrangements, amounts not offset in the condensed consolidated balance sheets, financial instruments	214	119
Derivative liabilities, under master netting arrangements, amounts not offset in the condensed consolidated balance sheets, collateral	1	(1)
Derivative liabilities, net amount	(322)	(40)
Over the Counter [Member] | Risk Management Derivatives [Member]
Assets
Derivative assets, gross amount	4,760	4,042
Derivative assets, gross amount offset	(4,737)	(4,021)
Derivative assets, net amount presented in the condensed consolidated balance sheets	23	21
Derivative assets, under master netting arrangements, amounts not offset in the condensed consolidated balance sheets, financial instruments	0	0
Derivative assets, under master netting arrangements, amounts not offset in the condensed consolidated balance sheets, collateral	0	(18)
Derivative assets, net amount	23	3
Liabilities:
Derivative liabilities, gross amount	(7,739)	(6,118)
Derivative liabilities, gross amount offset	7,580	5,861
Derivative liabilities, net amount presented in the condensed consolidated balance sheets	(159)	(257)
Derivative Liability, under master netting arrangements, amounts not offset in the condensed consolidated balance sheets, financial instruments	0	0
Derivative liabilities, under master netting arrangements, amounts not offset in the condensed consolidated balance sheets, collateral	0	0
Derivative liabilities, net amount	(159)	(257)
Exchange Cleared [Member] | Risk Management Derivatives [Member]
Assets
Derivative assets, gross amount	1,512	708
Derivative assets, gross amount offset	(1,417)	(3)
Derivative assets, net amount presented in the condensed consolidated balance sheets	95	705
Derivative assets, under master netting arrangements, amounts not offset in the condensed consolidated balance sheets, financial instruments	0	0
Derivative assets, under master netting arrangements, amounts not offset in the condensed consolidated balance sheets, collateral	0	0
Derivative assets, net amount	95	705
Liabilities:
Derivative liabilities, gross amount	(4,848)	(2,796)
Derivative liabilities, gross amount offset	4,843	2,789
Derivative liabilities, net amount presented in the condensed consolidated balance sheets	(5)	(7)
Derivative Liability, under master netting arrangements, amounts not offset in the condensed consolidated balance sheets, financial instruments	0	0
Derivative liabilities, under master netting arrangements, amounts not offset in the condensed consolidated balance sheets, collateral	5	0
Derivative liabilities, net amount	$ 0	$ (7)