Borrowings - Detailed Information on FHLB Advances and Other Borrowings (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Federal Home Loan Bank, Advances, Activity for Year
Maximum outstanding at any month end	$ 5,005	$ 5,740	$ 5,665
Average outstanding balance	3,064	4,713	4,590
Average remaining borrowing capacity	$ 4,194	$ 2,089	$ 1,195
Weighted average interest rate	1.90%	1.96%	1.30%