Guarantee Arrangements and Pledged Assets and Repurchase Agreements - Offsetting of Resale and Repurchase Agreements and Securities Borrowing and Lending Agreements (Details) - USD ($) $ in Millions		Jun. 30, 2018	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Securities purchased under agreements to resell, Gross Amounts Recognized		$ 12,919	$ 33,974
Securities purchased under agreements to resell, Gross Amounts Offset in the Balance Sheet	[1]	2,743	1,356
Securities Purchased under Agreements to Resell		10,176	32,618
Securities purchased under agreements to resell, Gross Amounts Not Offset in the Balance Sheet, Financial Instruments	[2]	10,171	32,616
Securities purchased under agreements to resell, Gross Amounts Not Offset in the Balance Sheet, Cash Collateral Receive / Pledged		0	0
Securities purchased under agreements to resell, Net amount	[3]	5	2
Securities sold under repurchase agreements, Gross Amounts Recognized		5,486	4,721
Securities sold under repurchase agreements, Gross Amounts Offset in the Balance Sheet	[1]	2,743	1,356
Securities sold under repurchase agreements, Net Amounts Presented in the Balance Sheet		2,743	3,365
Securities sold under repurchase agreements, Gross Amounts Not Offset in the Balance sheet, Financial Instruments	[2]	2,737	3,364
Securities sold under repurchase agreements, Gross Amounts Not Offset in the Balance Sheet, Cash Collateral Received / Pledged		0	0
Securities sold under repurchase agreements, Net amount	[3]	$ 6	$ 1

[1] Represents recognized amount of resale and repurchase agreements with counterparties subject to legally enforceable netting agreements that meet the applicable netting criteria as permitted by generally accepted accounting principles.

[2] Represents securities received or pledged to cover financing transaction exposures.

[3] Represents the amount of our exposure that is not collateralized / covered by pledged collateral.