Investment Securities - Held-to-Maturity Securities (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Investment securities transferred from HTM to AFS	$ 144,000,000
Purchase of HTM securities		$ 0	$ 0	$ 0
Collateral pledged
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, available-for-sale, restricted	$ 1,900,000,000	$ 874,000,000	$ 1,900,000,000