Investment Securities - Narrative (Details) $ in Millions	Jun. 30, 2020 USD ($)
FNMA investments
Debt Securities Exceeding Ten Percent of Stockholders Equity [Line Items]
Securities, amortized cost	$ 16,500
Securities, fair value	17,000
FHLMC investments
Debt Securities Exceeding Ten Percent of Stockholders Equity [Line Items]
Securities, amortized cost	12,000
Securities, fair value	$ 12,400