Derivative Financial Instruments Credit Derivative Instruments - TRS Contracts (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Credit Derivative Instruments - TRS Contracts [Line Items]
Derivative, Notional Amount	$ 255,352	$ 233,052
Derivative Asset, Fair Value, Gross Asset	3,518	2,631
Derivative Liability, Fair Value, Gross Liability	2,857	2,716
Total Return Swap [Member]
Credit Derivative Instruments - TRS Contracts [Line Items]
Derivative, Notional Amount	2,392	2,009
Derivative Asset, Fair Value, Gross Asset	37	97
Derivative Liability, Fair Value, Gross Liability	33	94
Collateral Already Posted, Aggregate Fair Value	$ 643	$ 601