Accounting Policies and Basis of Presentation Accounting Policies and Basis of Presentation (Recently Adopted Accounting Standards) (Details) - USD ($)		1 Months Ended	3 Months Ended
	Mar. 12, 2020	Apr. 30, 2020	Mar. 31, 2020	Mar. 31, 2019	Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stock issued (in shares)			339,958,000
Preferred stock, par value (in dollars per share)			$ 0.01			$ 0.01
Proceeds from Issuance of Preferred Stock and Preference Stock			$ 345,000,000	$ 0
Stock repurchased during period (in shares)			349,390	243,000
Stock repurchased during period			$ 159,704,000	$ 100,700,000
Stock repurchased during period (in USD per share)			$ 457.05	$ 414.58
Reserve for unfunded commitments			$ 10,500,000
Retained earnings			3,632,894,000			$ 3,658,197,000
Financing Receivable, Allowance for Credit Loss			209,259,000	$ 228,775,000		$ 225,141,000	$ 223,712,000
Subsequent Event
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stock repurchased during period		$ 37,300,000
Stock repurchased during period (in USD per share)		$ 333.71
Number of shares authorized to be repurchased (in shares)		500,000
Fixed-to-Floating Rate Subordinated Notes Due 2030
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt instrument face amount			$ 350,000,000
Interest rate (percentage)			3.375%
Shares issued on conversion (in shares)			0.025000
Liquidation preference per share (in USD per share)			$ 25
Non-Cumulative Perpetual Preferred Stock, Series A
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Dividend rate (percentage)			5.375%
Preferred stock, par value (in dollars per share)			$ 0.01
Liquidation preference per share (in USD per share)			$ 1,000
Depositary Shares
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stock issued (in shares)	13,800,000
Class A Common Stock
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stock repurchased during period				$ 100,756,000
Class A Common Stock | Subsequent Event
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stock repurchased during period (in shares)		111,700
Class A Common Stock | Repurchases From Ella Ann Holding
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stock repurchased during period (in shares)			45,000
Number of shares authorized to be repurchased (in shares)			250,000
Cumulative effect of adoption of ASC 326
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reserve for unfunded commitments					$ 8,900,000
Retained earnings					36,900,000
Financing Receivable, Allowance for Credit Loss					(37,900,000)
Cumulative effect of adoption of ASC 326 | Non-PCD Loans
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss					(56,900,000)
Cumulative effect of adoption of ASC 326 | PCD Loans
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss					$ 19,000,000.0