Financial Instruments Subject to Off-Balance Sheet Credit Risk or Concentration Risk (Offsetting Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Financial Instruments Subject to Off-Balance Sheet Credit Risk or Concentration Risk [Abstract]
Securities loaned, Gross Liabilities	$ 2,233	$ 1,477
Securities loaned, Net Amounts Presented in the Consolidated Balance Sheet	2,233	1,477
Securities loaned, Gross Amounts Not Offset in the Consolidated Balance Sheet, Counterparty Offsetting	(70)	(69)
Securities loaned, Gross Amounts Not Offset in the Consolidated Balance Sheet, Collateral	(1,990)	(1,293)
Securities loaned, Net Amount	173	115
Total Gross Liabilities	2,233	1,477
Total Liabilities, Net Amounts Presented in the Consolidated Balance Sheet	2,233	1,477
Total Liabilities, Gross Amounts Not Offset in the Consolidated Balance Sheet, Counterparty Offsetting	(70)	(69)
Total Liabilities, Gross Amounts Not Offset in the Consolidated Balance Sheet, Collateral	(1,990)	(1,293)
Total Liabilities, Net Amount	$ 173	$ 115