Investment Securities - Narrative (Details) - USD ($)	Jun. 30, 2020	Dec. 31, 2019
Schedule of Held-to-maturity Securities [Line Items]
Percentage of total securities	94.00%
Unrealized credit losses	$ 0	$ 0
Other assets	1,200,000,000	930,000,000
Accrued interest receivable on investment securities
Schedule of Held-to-maturity Securities [Line Items]
Other assets	$ 6,000,000	$ 6,000,000