Derivative Financial Instruments - Fair Value Hedges (Details) - Interest rate swaps - Other assets - Derivatives designated as hedging instruments $ in Millions	Sep. 30, 2021 USD ($)
Derivative [Line Items]
Amortized Cost Basis of the Hedged Assets	$ 17,524
Cumulative Amount of Fair Value Hedging Adjustment Included in the Carrying Amount of the Hedged Assets (2)	(13)
Amortized cost of hedged items where the hedged item is the last layer expected to be remaining at the end of the hedging relationship	13,400
Amount of hedged items where the hedged item is the last layer expected to be remaining at the end of the hedging relationship	7,300
Cumulative adjustments of hedged items where the hedged item is the last layer expected to be remaining at the end of the hedging relationship	13
Hedged Asset, Discontinued Fair Value Hedge, Cumulative Increase (Decrease)	$ 6