Borrowings - Detailed Information on FHLB Advances and Other Borrowings (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Debt Disclosure [Abstract]
Maximum outstanding at any month end	$ 5,595	$ 4,388	$ 5,595	$ 6,841
Average outstanding balance	4,080	3,528	3,894	4,234
Average remaining borrowing capacity	$ 5,705	$ 5,494	$ 5,495	$ 5,249
Weighted average interest rate	0.42%	0.48%	0.43%	0.76%