Derivative Financial Instruments Netting of Financial Instruments - Derivatives (Additional Information) (Details) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative Asset	[1]	$ 657	$ 802
Derivative Asset, Collateral, Obligation to Return Cash, Offset		408	371
Derivative Liability	[2]	580	408
Derivative Liability, Collateral, Right to Reclaim Cash, Offset		916	1,303
Trading Securities [Member]
Derivative [Line Items]
Derivative Asset		657	802
Trading Liabilities [Member]
Derivative [Line Items]
Derivative Liability		$ 580	$ 408

[1] At March 31, 2018, $657 million, net of $408 million offsetting cash collateral, is recognized in Trading assets and derivative instruments within the Company's Consolidated Balance Sheets. At December 31, 2017, $802 million, net of $371 million offsetting cash collateral, is recognized in Trading assets and derivative instruments within the Company's Consolidated Balance Sheets.

[2] At March 31, 2018, $580 million, net of $916 million offsetting cash collateral, is recognized in Trading liabilities and derivative instruments within the Company's Consolidated Balance Sheets. At December 31, 2017, $408 million, net of $1.3 billion offsetting cash collateral, is recognized in Trading liabilities and derivative instruments within the Company's Consolidated Balance Sheets.