Regulatory Capital - Additional Information (Details)		3 Months Ended		9 Months Ended
	Jan. 01, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Allowance for credit losses on loans and leases		$ 1,215,407,000	$ 1,734,559,000	$ 1,215,407,000	$ 1,734,559,000	$ 1,160,244,000	$ 1,361,723,000	$ 1,929,323,000	$ 441,912,000
Ending balance		99,131,000	114,778,000	99,131,000	114,778,000	$ 64,772,000	$ 110,044,000	$ 85,958,000	$ 2,481,000
Dividends		$ 50,000,000	$ 0	$ 1,200,000,000	$ 568,000,000
Accounting Standards Update 2016-13
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Period of deferment	2
Amount deferred	25.00%
Allowance for credit losses on loans and leases	$ 1,100,000,000
Ending balance	116,000,000
Deferred tax assets	306,000,000
Reduction to retained earnings	$ 953,000,000