Investment Securities (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Mar. 31, 2020
Schedule of Held-to-maturity Securities [Line Items]
Securitized HFS loans not sold	$ 0	$ 2,058,000,000
Other than temporary impairment	0
Other assets	930,000,000	$ 1,430,000,000
Federal Government
Schedule of Held-to-maturity Securities [Line Items]
Percentage of total securities		95.00%
Accrued interest receivable on investment securities
Schedule of Held-to-maturity Securities [Line Items]
Other assets	$ 6,000,000	$ 7,000,000