Securities Financing Arrangements (Offsetting Financing Assets and Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Derivative assets
Gross Amounts of Recognized Assets/Liabilities	$ 1,322	$ 1,626
Gross Amounts Offset in Balance Sheet	607	770
Net Amounts Presented in Balance Sheet	715	856
Gross Amounts Not Offset In Balance Sheet, Financial Instruments	25	20
Gross Amounts Not Offset in Balance Sheet, Cash Collateral Received/Pledged	0	0
Net Amount	690	836
Securities borrowed or purchased under resale agreements
Gross Amounts of Recognized Assets/Liabilities	31,845	31,386
Gross Amounts Offset in Balance Sheet	10,951	11,639
Net Amounts Presented in Balance Sheet	20,894	19,747
Gross Amounts Not Offset in Balance Sheet, Financial Instruments	20,816	19,657
Gross Amounts Not Offset in Balance Sheet, Cash Collateral Received/Pledged	0	0
Net Amount	78	90
Total Financial Assets
Gross Amounts of Recognized Assets/Liabilities	33,167	33,012
Gross Amounts Offset in Balance Sheet	11,558	12,409
Net Amounts Presented in Balance Sheet	21,609	20,603
Gross Amounts Not Offset In Balance Sheet, Financial Instruments	20,841	19,677
Gross Amounts Not Offset in Balance Sheet, Cash Collateral Received/Pledged	0	0
Net Amount	768	926
Derivative liabilities
Gross Amounts of Recognized Assets/Liabilities	1,127	1,684
Gross Amounts Offset in Balance Sheet	620	1,047
Net Amounts Presented in Balance Sheet	507	637
Gross Amount Not Offset in Balance Sheet, Financial Instruments	142	176
Gross Amounts Not Offset in Balance Sheet, Cash Collateral Received/Pledged	0	5
Net Amount	365	456
Securities loaned or sold under repurchase agreements
Gross Amounts of Recognized Assets/Liabilities	37,388	36,255
Gross Amounts Offset in Balance Sheet	10,951	11,639
Net Amounts Presented in Balance Sheet	26,437	24,616
Gross Amounts Not Offset in Balance Sheet, Financial Instruments	25,639	23,812
Gross Amounts Not Offset in Balance Sheet, Cash Collateral Received/Pledged	0	0
Net Amount	798	804
Total Financial Liabilities
Gross Amounts of Recognized Assets/Liabilities	38,515	37,939
Gross Amounts Offset in Balance Sheet	11,571	12,686
Net Amounts Presented in Balance Sheet	26,944	25,253
Gross Amount Not Offset in Balance Sheet, Financial Instruments	25,781	23,988
Gross Amounts Not Offset in Balance Sheet, Cash Collateral Received/Pledged	0	5
Net Amount	$ 1,163	$ 1,260