Financial Instruments Subject to Off-Balance Sheet Credit Risk or Concentration Risk (Offsetting Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Offsetting Assets [Line Items]
Resale agreements, Gross Asset	$ 9,547	$ 8,088
Resale agreements, Net Amounts Presented in the Consolidated Balance Sheets	9,547	8,088
Resale agreements, Gross Amounts Not Offset in the Consolidated Balance Sheets, Collateral	(9,547)	(8,088)
Resale agreements, Net Amount	0	0
Securities borrowed, Gross Asset	393	198
Securities borrowed, Net Amounts Presented in the Consolidated Balance Sheets	393	198
Securities borrowed, Gross Amounts Not Offset in the Consolidated Balance Sheets, Counterparty Offsetting	(200)	(70)
Securities borrowed, Gross Amounts Not Offset in the Consolidated Balance Sheets, Collateral	(189)	(127)
Securities borrowed, Net Amount	4	1
Total Gross Assets	9,940	8,286
Total Assets, Net Amounts Presented in the Consolidated Balance Sheets	9,940	8,286
Total Assets, Gross Amounts Not Offset in the Consolidated Balance Sheets, Counterparty Offsetting	(200)	(70)
Total Assets, Gross Amounts Not Offset in the Consolidated Balance Sheets, Collateral	(9,736)	(8,215)
Total Assets, Net Amount	4	1
Fair value of client securities available to be pledged	$ 21,516	$ 22,385
Resale And Repurchase Agreements [Member]
Offsetting Assets [Line Items]
Percentage of collateral to related assets	102.00%	102.00%
Fair value of client securities available to be pledged	$ 9,800	$ 8,200