Investment Securities - Narrative (Details) $ in Millions	Jun. 30, 2021 USD ($)
Debt Securities Exceeding Ten Percent of Stockholders Equity [Line Items]
Debt Securities, Available-for-sale, Allowance for Credit Loss	$ 0
FNMA investments
Debt Securities Exceeding Ten Percent of Stockholders Equity [Line Items]
Securities, amortized cost	37,600
Securities, fair value	37,400
FHLMC investments
Debt Securities Exceeding Ten Percent of Stockholders Equity [Line Items]
Securities, amortized cost	41,400
Securities, fair value	$ 41,100