Summary of Significant Accounting Policies (Details) $ in Billions	12 Months Ended
	Dec. 31, 2020 USD ($) state segment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of states in which entity operates | state	11
Number of community regional banks operating in distinct geographical areas | segment	7
Percentage of agreements with minimum maturity period	28.00%
Percentage of agreements with maximum maturity period	0.00%
Securities for which entity has right to sell or repledge	$ 5.7
Security resell agreements average amount	2.1
Security resell agreements maximum amount, outstanding	$ 6.4
Percentage of acquired assets and all assumed liabilities recognized in business combination	100.00%
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Security resell agreements maturity (in days)	30 days
Minimum | Building
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful lives of properties (in years)	25 years
Minimum | Furniture and Equipment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful lives of properties (in years)	3 years
Minimum | Software
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful lives of properties (in years)	3 years
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Security resell agreements maturity (in days)	50 days
Maximum | Building
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful lives of properties (in years)	40 years
Maximum | Furniture and Equipment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful lives of properties (in years)	10 years
Maximum | Software
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful lives of properties (in years)	10 years