Borrowings - Detailed Information on FHLB Advances and Other Borrowings (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Debt Disclosure [Abstract]
Maximum outstanding at any month end	$ 4,388	$ 2,979	$ 6,841	$ 3,391
Average outstanding balance	3,528	2,446	4,234	2,769
Average remaining borrowing capacity	$ 5,494	$ 4,957	$ 5,249	$ 3,932
Weighted average interest rate	0.48%	2.10%	0.76%	2.33%