Guarantee Arrangements and Pledged Assets and Repurchase Agreements - Offsetting of Resale and Repurchase Agreements and Securities Borrowing and Lending Agreements (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Securities purchased under agreements to resell, Gross Amounts Recognized		$ 33,974	$ 30,784
Securities purchased under agreements to resell, Gross Amounts Offset in the Balance Sheet	[1]	1,356	761
Securities Purchased under Agreements to Resell		32,618	30,023
Securities purchased under agreements to resell, Gross Amounts Not Offset in the Balance Sheet, Financial Instruments	[2]	32,616	29,945
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]	2	78
Securities sold under repurchase agreements, Gross Amounts Recognized		4,721	4,433
Securities sold under repurchase agreements, Gross Amounts Offset in the Balance Sheet	[1]	1,356	761
Securities sold under repurchase agreements, Net Amounts Presented in the Balance Sheet		3,365	3,672
Securities sold under repurchase agreements, Gross Amounts Not Offset in the Balance sheet, Financial Instruments	[2]	3,364	3,661
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]	$ 1	$ 11

[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.