Investment Securities - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Investments, Debt and Equity Securities [Abstract]
sale of securities	$ 33,200
FNMA investments
Debt Securities Exceeding Ten Percent of Stockholders Equity [Line Items]
Securities, amortized cost	16,100
Securities, fair value	16,200
FHLMC investments
Debt Securities Exceeding Ten Percent of Stockholders Equity [Line Items]
Securities, amortized cost	11,800
Securities, fair value	$ 11,900