Derivative Financial Instruments - Carrying Amount and Cumulative Basis Adjustments for Hedge Accounting (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Hedged Items Currently Designated | Long-term debt
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Carrying Amount of Hedged Assets/Liabilities	$ 9,023	$ 10,519
Cumulative Hedge Accounting Basis Adjustments	(7)	3
Hedged Items Currently Designated | Investment securities available-for-sale
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Carrying Amount of Hedged Assets/Liabilities	3,756	2,330
Cumulative Hedge Accounting Basis Adjustments	18	2
Hedged Items No Longer Designated | Long-term debt
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Cumulative Hedge Accounting Basis Adjustments	595	688
Hedged Items No Longer Designated | Investment securities available-for-sale
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Cumulative Hedge Accounting Basis Adjustments	$ 33	$ 43