Derivative Financial Instruments Netting of Financial Instruments - Derivatives (Additional Information) (Details) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Document Period End Date		Sep. 30, 2019
Derivative Asset	[1]	$ 1,770	$ 639
Derivative Asset, Collateral, Obligation to Return Cash, Offset		358	338
Derivative Liability	[2]	274	410
Derivative Liability, Collateral, Right to Reclaim Cash, Offset		(1,007)	(652)
Trading Assets [Member]
Derivative [Line Items]
Derivative Asset		1,800	639
Derivative Liability, Collateral, Right to Reclaim Cash, Offset		(1,000)
Trading Liabilities [Member]
Derivative [Line Items]
Derivative Liability		$ 274	$ 410

[1] At September 30, 2019, $1.8 billion, net of $358 million offsetting cash collateral, is recognized in Trading assets and derivative instruments within the Company's Consolidated Balance Sheets. At December 31, 2018, $639 million, net of $338 million offsetting cash collateral, is recognized in Trading assets and derivative instruments within the Company's Consolidated Balance Sheets.

[2] At September 30, 2019, $274 million, net of $1.0 billion offsetting cash collateral, is recognized in Trading liabilities and derivative instruments within the Company's Consolidated Balance Sheets. At December 31, 2018, $410 million, net of $652 million offsetting cash collateral, is recognized in Trading liabilities and derivative instruments within the Company's Consolidated Balance Sheets.